Due to time constraints, my reviews for Flatbeds of Fear, Disappearing Diesels, Signals Crossed, Toad's Adventure, and Duck in the Water will be much shorter.

If you want to read my other S18 reviews:

1. Thomas the Quarry Engine (old, U.S.)
   
2. Old Reliable Edward (U.K.)
   
3. Not So Slow Coaches (U.K.)
   
4. Duck and the Slip Coaches (U.K.)
   

Flatbeds of Fear:

Strengths:

1. The three strikes were used effectively. They were obvious, but developed the story nicely.
   
2. The animation gave the audience extremely effective clues to what caused the whirring noise.
   
3. Thomas, Emily, Salty, and Cranky were in character.
   
4. "I don't want to hear the Flatbeds of Fear." The rhyming has been something many older fans don't want to hear because previous seasons really abused it, but this is a case that worked to prevent Henry from losing his boiler.
   
5. The beginning and ending set the mood. It was a clever plot device by having the flatbed roll the camera in and out, thus beginning and ending the story respectively.
   
6. Use of longer words: "sensible explanation." I'll get to this in a minute in the weakness section.
   

Weaknesses:

1. "Sensible explanation" was repeated way too many times. Vary the vocabulary.
   
2. Although the Rule of Thirds was used effectively, they were still pretty obvious. This is especially the case for the next point.
   
3. Henry was out of character. The old "worrywart" personality from Henry doesn't fit him one bit. By using characterization that doesn't fit the character, the plotline becomes contrived.
   
4. One of The Afternoon Tea Express's biggest issues is the overreliance on the narrator. The same quality flaw applies here. Instead of the narrator saying the driver pulled him to the siding, how about letting the driver stop at the danger signal and ask Henry what was wrong? When Henry says the sound's making him scared, and he won't move, he asks the stationmaster to let them in on the siding.
   
5. The "ghost story" isn't exactly that spooky. If anything, it feels incredibly short. Right away, we can tell this doesn't feel like a ghost story because we can assume otherwise. What makes the flatbeds of fear so spooky? Did it fall off a bridge, crash into a mine, derail, sink through the ground, or crash into a train behind them? Make it feel scary.
   
6. This episode relies on a major cliché in entertainment: "The character is skeptical until he or she hears something that caused them to be skeptical of. He or she starts to believe it until someone reveals the root to the problem."
    
   Also, the fact that Cranky didn't clamp on the story did nothing except make the conflict too long.
   

Without a doubt, the weakest story of the season. But not the worst. That I'll get to later.

Disappearing Diesels:

Strengths:

1. "Some engines on the Island of Sodor give diesels a bad reputation." Extremely effective for two reasons.
   1. 
      
   2. Diesel is an antagonist and is one of the diesels responsible for giving his style of engine a bad reputation. Him doing something cruel like shunting trucks into Percy gets the message down quickly.
      
   3. "Reputation." Great and effective use of vocabulary. The opening shows why, and the word isn't used again the rest of the episode.
      

[*]Having Paxton be the other end of the spectrum gives the audience Diesel's foil. Diesel is an antagonist, while Paxton's loyalty to both diesels and steam locomotives and gentle personality bridges the tiring cliché between the two sides.

[*]Unlike FoF, DD doesn't overtly rely on Moraghan telling the audience everything. There's quite a bit of silence in the episode, particularly the first chase sequence between Brendam Docks and the Scrapyard on Edward's branch line.

[*]Compare the vocal performance of Kerry Shale (the UK voice) and Martin Sherman (the new US voice). Sherman was the most natural. Shale's voice acting came off as rather weak, as if trying to convey emotion but couldn't. Contrastly, Sherman did an excellent job portraying Diesel's deviousness, antagonism, despair, and confusion.

[*]Reg only spoke a few lines, but there's plenty of personality, so he didn't need to do any more.

[*]"I'm a truckload of sausages!" Talk about a very clever reference to Dirty Work/Diesel's Devious Deed. LOL!

[*]There are two important morals:

1. Just because you play a joke doesn't make it funny.
   
2. Don't take kindness for granted.
   

Conceptually, it makes sense to use both characters. Diesel is the kind of character to play such an insensitive trick to a lovable goofball like Paxton. Paxton, meanwhile, is a very sensitive character who cares for every engine.

Weaknesses:

1. This episode follows the structure of The Lost Puff perfectly. Even without the moral and chase, you get the gist of the structure: "Paxton knows something is wrong and roams throughout the island trying to locate something." In The Lost Puff, it was the "puff." Here, it's missing diesels.
    
   Besides, the "hiding" places were really stupid. Paxton chuffs by Sidney despite being in full sight, while he barely pulls up to two trains with a diesel as a header before backing up. If you're going to make Paxton worried, make the hiding spots convincing like Dart being lifted off the ground.
    
   Like what SkarloeyRailway01 and the main SIF review suggested, why not have Paxton just do his job instead? He can worry about the diesels, but they slowly dissipate as Rusty, Salty, and the others appear one by one.
   
2. The second the narrator told the audience Paxton needed to refuel, it became predictable really fast. You know somewhere down the line (pun intended), Diesel would run out of fuel. By making it predictable, you suck the investment out of the story.
   
3. The three kids standing on the crossing gates is a major no-no. No matter how much people don't get bothered by it, it's extremely dangerous to stand on it. Having them watch from anywhere else like a train station, bridge, or on the ground behind the level crossing would've worked much better. The only reason this isn't worse than Thomas quickly switching points in Old Reliable Edward is because the gates scene was incidental and doesn't impact the episode whatsoever.
   

Despite its shortcomings, it's actually a pretty good episode.

Signals Crossed:

Strengths:

1. As far as the concept is concerned, Toby's fear was in character this time. To quote my last post (with a change or two):
    

   
   I could harp on Toby's case of fear. Like what jjlr said, over the past several seasons, the Tram Engine has been hit with the Worry Stick at the most inopportune times for the most stupid reasons like the Whistling Woods or even a whistle, flanderizing him from the careful and wise character he was known for.
    
   Here, Toby's worry is much more in character conceptually for one big reason: It's justifiable. Knapford Junction (the newest and most complex addition to the series) is extremely gigantic and bustling, and the Big Station is actually treated as the Big Station. Unlike previous episodes (because it was simply a few rows of track), there's more emphasis on the calamity of the morning traffic. When you have so many big engines ramming through, it makes Toby look much smaller than normal. He wants to pick up the quarrymen, but the massive convolution of the signal rows make him fearful of picking up the wrong signal and thus getting into a nasty accident. With all of these big and little details, it turns what should be a routine morning into a major nightmare.

   There's been commentary about being afraid of the signals. He wasn't afraid of the signals; he was afraid of being run into because the convoluted Signal Gantry would cause him to get run over.
    
   But pay attention to "conceptually." I'll get back to this later.
   
2. There's a really gigantic redesign of Knapford's front. I wrote this a while back, and I need to do it again.
    

   
   You can definitely tell that Arc has seriously improved since last season just by the visuals of Knapford alone. This is a massive overhaul of the station's presentation, which has all but stayed the same throughout Thomas & Friends's thirty-year history. Previously, the look is basically the model railway in animated form. With this overhaul, Arc completely takes advantage of its tools, further separating itself from the model era and incorporating much more realism. It's extremely refreshing, and it further hones in how the CGI is progressively becoming a part of the story.

   It was no surprise to see the gantry become an active role.
   
3. Speaking of active, if going by UK canon, SC is Henrietta's first speaking role in the show since 1986. Here, she plays her most active role by far. While Toby's confused and later frightened, Henrietta plays the grandmother, reassuring Toby while being impatient herself and taking no nonsense when James antagonizes them.
    
   To summarize it, Henrietta almost stole this episode because her characterization was fully realized.
   
4. There's way more human activity here in this episode. The quarrymen pressure Toby to move, while one of TFC's bodyguards whispers about the the broken signal, telling the viewers there's more to Sodor than trains and rolling stock.
   

Weaknesses:

1. Toby's fear is in character conceptually, but his response is not. Toby is an engine capable of standing up to himself and taking no crap from anyone. There's no need for him to suddenly hide behind a signalbox, lie to Henrietta and Thomas, and than have them result in swallowing his pride and confronting the signal.
    
   (This is one episode where having the driver and fireman active would've helped out. Unfortunately, his "character development" would've fallen apart if they did and make the whole episode shorter than the four-and-a-half-minute version.)
    
   Also, it's a shame he didn't call out James for biffing him and Henrietta. Doing this would've allowed the writers to edge Toby closer and closer to his true character.
   
2. Three important characters were seriously unlikeable. Gordon, James, and The Fat Controller all talk to Toby like he's senile, tender, or new to the Island. They know how long Toby's lived there. Despite some very loose continuity, he's lived on Sodor since the first season. The REAL Toby knows his way around Sodor and wouldn't tolerate being talked down like that.
    
   Gordon may be impatient and pompous, but he's WAY too rude here, especially to a longtime friend.
    
   James bullies his way through Knapford and suffers no consequences for his dangerous actions. "I'll be running late" is no excuse for derailing his character.
    
   TFC babies him and has the Idiot Ball for a brain. Instead of immediately trusting Toby's instincts, the bodyguard had to act as a get-out-of-jail-free card to rush the ending.
   
3. There's far too much repetition. You have the "You're the number seven brown tram engine," "Lookout! You silly old/little tram! And learn your signals," "I'm just a little steam tram," and "Everyone knows you're afraid of Knapford Junction." There's more to attracting your market audience than by reiterating phrases over and over again.
   
4. Knapford is supposed to be the Big Station, but HiT and/or Arc really overexaggerated its hustle and bustle. If you want to hone in the story, at least give Toby and Henrietta a small break and the opportunity to cross. It's one thing to make Knapford Junction overwhelming. It's another to make the overwhelming feeling become cumbersome.
   
5. The fact that Knapford Junction was retconned as a permanent setting for a long time is a big mistake by the writing team. By how the script tells the story, it's saying the old style of track was either never truly a thing or something that's been around for several years. If there was more backstory to how and when Knapford Junction was built, then you could delve further and have the team bridge the gap, Toby's overall fright, and the characters' responses to his confusion.
    
   This is why his fear is in character conceptually. By having this episode implicate Knapford Junction's a longtime, permanent standpoint in the series, Toby's fear feels extremely artificial: Since so many engines know how timid he feels towards it, wouldn't it make much more sense to have anybody confront him about it a long time ago?
   

At this point, Flatbeds of Fear may be the weakest S18 episode. But Signals Crossed is objectively the worst one because it's a mess.

Toad's Adventure:

Strengths:

1. Toad and Oliver are in character, and their West Country accents match their personalities perfectly. Oliver is puffed up in the smokebox by continually telling his story about arriving on Sodor. Toad was annoyed, and his desire to work hard works. It makes plenty of sense to see them act the way they did.
   
2. Great comedy with Toad's and James's dialogue bouncing off each other. (Nice wink to the Little Western branchline, BTW.)
   
3. This episode fixes the biggest flaw from Series 5's Busy Going Backwards (Toad's guard jumping clear when the Trucks broke loose). The guard left his cab and slammed his breaks hard. Even though the guard didn't speak, his involvement and Toad's utter concentration on not crashing made it a really big improvement.
    
   (I do, though, wish he shared credit, but that's nitpicking.)
   
4. James was in character, too. Unlike most episodes this season, he wasn't an antagonist. He just ignored Toad's warning, causing him to be as puffed up, too. But he did learn his lesson, got the load to Vicarstown, and began a god friendship with the breakvan. It was pretty funny, too, for him to tell Oliver about his adventure on Gordon's Hill.
   
5. Robert Hartshorne doesn't get much credit for his music in my reviews despite being consistently top-notch over the past several years. Well, changing that here, as his fantastic score once James's couple got dislodged and the near crash accentuated the tension and made it extremely nerve-wracking to watch.
    
   And then…ping.
   
6. Dowager Hatt is absolutely hilarious with her terrible opera singing. Even funnier by being completely oblivious to the fact.
   
7. Arc and HiT get credit for allowing engines from all eras to gather around while Toad tells his story. Like it or not, these characters are part of the overall railway scope, and ignoring them does nothing except unnecessarily retcon the show. It has a long, rich history albeit very rough, and it'd be stupid to ignore it. Major kudos there.
   

Weaknesses:

1. The episode behaves as if Toad never had an adventure of his own before. This was one of BGB's plot points. Toad wanted to go forwards and underwent a massive, tumultuous adventure down the mainline. It risks breaking continuity.
   
2. Thomas was shoehorned into the episode. You could've plugged in any other engine, and nothing would've changed.
   
3. The whole peril is completely pointless.
    
   Gordon's Hill doesn't have any trees that close.
    
   If James rolled over the thick branch, it would either crunch under his heavy wheels and/or derail the train.
    
   The "one engine per section" rule was blatantly violated and plugged in simply to highlight Toad's strong breaks and cause the peril.
   

As a whole, a small improvement over Busy Going Backwards, but still rather rough along the edges.

Duck in the Water (unofficial/essay format):

Now THIS is what I expected to see. After how bad Signals Crossed was, Toad's Adventure did well, but Duck in the Water is where Series 18 gets right back on the rails.

Just to get it out of the way, this is the first Thomas episode since The Switch to not feature Thomas anywhere. Not even a cameo. This is a very good thing because you don't need to pander to your market audience by plugging in the most popular character everywhere you go. Moreover, it's the first episode in a LONG time to feature Duck's branch line.

Compared to his flanderization in SC, James is actually in character here. Sure, he's an antagonist here, but there's a much more solid explanation based on who he is (vain, cheeky, temperamental, impatient) and his justification (yearn for importance and belief that pulling trucks was below his strict standards).

One of the bigger bugaboos in this episode is how Rocky kept swinging back and forth as James raced down Duck's branchline. I'm all for having Rocky swinging, but the animation emphasized it way too much. Rocky's a crane on Sodor, not a toy, and he swung like gusts of wind pushed him around. Moreover, James's crew shouldn't be so stupid in blatantly ignoring Rocky's cries for help; they operate the train for a reason, you know.

Instead, how Rocky was stationary except when there's either a curve or have be improperly secured, which causes him to get his arm loose and knock the signal down? But if there's one thing this strike did, it gained a nice (albeit artificial) payoff: The grand narrative treated James's recklessness as wrong, hence the confusion and his consequences.

The morals themselves work very well, even better by how they're organic and not hammered in:

1. You're not going to do everything you like.
   
2. Better to be safe and steady with dangerous work than quick and impatient.
   
3. If you make a mistake, own up to it.
   

Typically, winter on the Island is depicted as beautiful, cozy, and perfect. Arc really changed the mood and made it more realistic by making the winter somewhat warmer, bleaker, and gray, reversing the cliché. Plus, it works great narratively, for it allows Arc and Brenner to develop the conflict more organically.

Then you have the dialogue. There's plenty of life in the characters: TFC, James, Duck, and Rocky delivered plenty of lines to blend together and create cohesive chemistry. Of course, the comedy is rather top notch, and there are many well-done visual and verbal gags, like James's cheeky pun to TFC of all people, Duck's glum gaze at the ducks, and James's increasing embarrassment when confronted by TFC.

Compared to most stories this season, it's much simpler and focuses on slice of life with a little bit of adventure on the side. Sure, the adventure exists, but it's far more character-driven than anything else, hence the backseat on the action.

Lastly, here's the synopsis:

When Duck gets stuck on some flooded track, James is sent to fetch Rocky to rescue him. But James does not wait for Rocky to secure his crane arm and they end up knocking down a signal before they arrive at the accident site! Without a signal to warn them, the other engines do not stop, and what began as a small accident soon escalates into a much bigger one involving several engines!

A response to the summary: The written previews don't do a very good job creating the anticipation of a really big accident. It took the expectations and reversed them. I don't know who submitted them, but whoever did needs to jot down a pen and write a more accurate synopsis. But this isn't a strike to the episode because the episode didn't set up those expectations.

So, Duck in the Water is one of the better episodes of Series 18 at the point of airing, but let's see how well it holds up.