If you want to read my first impressions of the episode, check out the spoilers:

After re-watching it, the episode has since really grown on me, and I began to embrace it more and more. Now I detail a few more things I adored:

1. Of all the episodes this season that featured the entire Mane Six cast, this is easily the strongest. Each line from the characters worked to perfection. Rarity, Applejack, Rainbow Dash, Pinkie, Twilight, and Spike had great and in-character lines. Celestia, for her brief moment, was great. Discord's antics and lines stole the episode.
   
2. The foul language from the critters. Of the Mane Six, Fluttershy is the only one who's been able to communicate and understand the creatures (the lone exception being Hell's Angel, strangely enough). Her being a median for both Applejack and the beaver was cute and hilarious.
   
3. Everyone but Fluttershy NOT trusting him, even completely all the way through the episode. Everyone was absolutely apprehensive about his revival and "reformation." Although Discord is starting to learn the error of his ways, it's obvious they still don't fully trust him. Even Celestia is still uncomfortable having him around, hence her stern whisper. This works really well because if everypony began to trust Discord off a drop of the dime, it would be way too sudden. It's going to take much more time before Discord can be fully relied on. DHX, writers, I'm counting on you to show some more development between him and the rest of the cast.
   
4. Discord still being the Spirit of Chaos, but not to the point of being a true villain. Of the four villains throughout the series, Discord has the most potential because of his charisma and depth in character. His tricks can still drive everyone angrier than the Angry Beavers, but still be both a protagonist and anti-hero. This draconequus has so much depth and can really give the canon so much worldbuilding. Furthermore, even more character development for Discord himself. More of this, the better!
   
5. The occurrence of one-shot characters returning to the scene. Like I said with Babs Seed in my analysis for Apple Family Reunion, we're seeing one-shot characters returning and hopefully receiving more of a role in the canon. Trixie, then Babs, and now Discord. I'd like to see more of this in the future, and hopefully more of Discord later this season and beyond.
   
6. The hilarity. Discord's tricks work so well and fit him so excellently. I was laughing a lot from his antics, particularly him taking out his eyeballs, rolling down the red carpet, reformatting Fluttershy's couch, and the dancing candles akin to Beauty & the Beast's "Be Our Guest."
   
7. The Deus Ex Machina being defeated early. Too Many Pinkie Pie's biggest flaw came midway in the plot, which was Spike discovering the book from inside a secret cupboard that led to the Legend of the Mirror Pond. The trick of Twilight forcing Discord to reform (only to have it being eaten) was an extremely clever and hilarious take in poking fun at this plot device.
   
8. Discord's plan to manipulate Fluttershy into having her promise not to use the Elements of Harmony against him, only to have this plan both work AND fail. When he was released, he composed a plan to fool and trick Fluttershy and take advantage of her kindness and assertiveness. All of those tricks were used in order to embarrass and humiliate her friends and convert her to his side. However, in the dinner party, he began to enjoy her company, and he was starting to at least have a heart for friendship, for his heart was as cold as stone. This enjoyment of her company made him spill those lines and compassion. The game he played worked for him, but also against him. "Well-played, Fluttershy. Well-played" is the best line in the entire episode (perhaps the entire season, with the exception of "I quit!" from Rainbow Dash and that line from Granny Smith in Apple Family Reunion dictating the possibility of not having so many family members attending the next reunion) and put his change of heart into full circle. But his stone cold heart wouldn't warm up without some hints, which is what I'm going to deliver next.
   
9. The foreshadowing. So much of it. It wasn't one surprise to another. Each event led to another and made the episode feel complete. Here's what I mean:
   
10. The Angry Beaver who didn't give a dam about Applejack's farm. This event hinted the huge dams and flood later in the episode.
    
11. Discord's sneaky trick with his tail. When he snapped his fingers, the beavers were put under a trance, and they built the dams that flooded Sweet Apple Acres (which Discord later froze into a lake of ice).
    
12. Discord eating the paper. This foreshadowed Twilight's plan to forcefully reform Discord, and he was one step ahead of her plan. When Twilight and the others left, they conversed on a backup plan to forcefully reform him in front of Fluttershy's door. Twilight said she had that plan. I wouldn't be surprised if Discord heard them and, with his magic, stole the spells and ate the paper.
    
13. Fluttershy declaring Discord as a friend. Discord intended to be buddy-buddy with her, but Fluttershy's words to Discord were kind and sincere. For a cold character such as Discord, it's something that he almost never hears and notices: actual warmth in conversation and belief that his exterior and treacherous trickery can be broken down by kind words and attitude. But he still manipulated the Mane Six and severed his trust she had for him. That line he spilled as Fluttershy rejected his manipulation and stormed off broke down the last bits of that block of cement and put that moment in the dinner party to full circle.
    

But there was one big flaw in this story, and it's completely the opposite of Spike at Your Service: The pace was too fast. From the get-go, the momentum was extremely quick, whereas Spike at Your Service had a great pace but a poor plot and even worse characterization of Spike. The runner broke into a sprint on the treadmill and, for the duration of the show, never slowed down. Writing a great pace for a storytelling is a lot like aerobic exercising. You start the pace slow and then you slowly build up your momentum and energy. Then, for one to two minutes, you race and make your heart beat quickly. Then you slow down again and change the pace and intensity here and there. In addition, you breathe to let the oxygen flow. Just like the person in his exercise routine, Keep Calm and Flutter On held his breath, then exhaled for a quarter of a second, and suddenly held it in for another minute. This kept on going, and this plot had no time to breathe and actually calm down for a few moments.

Discord's redemption would've been much better if the plot was slowed down, altered, split into two parts, and have the duration of his redemption last for more than just twelve hours. Instead of constant rapid and quick sequences to the point where the viewer can't fully grasp at the actions and consequences during the episode, slow down the pace a bit and space out the chaos to where we have calm in between the storm. Have Fluttershy converse with the others and maybe have a scene where Discord can talk about his coldness and love to make lives hell. Maybe have him create some chaos, but then think otherwise and keep the magic chaotic but fun. He can still have his moments, but he will feel warmer to the others and vice-versa. The development of Discord's friendship with Fluttershy would feel more natural and not as compacted as a tall man squeezing inside a Volkswagen Beetle.

That said, there were numerous great things that still made this episode strong. With great characterization, the episode flowed from one moment to another, and there was plenty of foreshadowing that and Fluttershy was the best candidate to penetrate Discord's stone-cold heart. He is much more relaxed and will no longer be transformed into a stone statue anymore, but he will likely remain the Spirit of Chaos that will hopefully drive everyone crazy and create some great chemistry with the other characters. The pace was abnormally quick, but it didn't deter what was an extremely exciting episode that hopefully takes advantage of Discord's great potential as an anti-hero and character altogether.

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Source: S03:E10 - Keep Calm and Flutter On