Warning: Spoilers for The Times They Are a Changeling. Read at your own risk.

A really big weakness in the first four-plus seasons was Spike's characterization. Examples include turning him into an unfunny victim of comedy "because Spikabuse is so funny"; derailing him into an greedy, dumb, and/or antagonistic shell of himself; shifting (all of) the blame to him; and being the star of some awful episodes when he's really good. When he's good, it's normally when he's a secondary character. Pre-S6, his best roles were Lesson Zero and EQG1. Yet, when he's the star, something happens for reasons I don't know. It's like they didn't know what to do with him and write an episode while tagging his name on the paper. Examples include:

1. Owl's Well: Make Spike feel jealous even though he has very good reasons to believe he's being replaced.
2. Dragon Quest: His best characterization as a mane character, yet it fails for unfortunate implications and usage of horrible stereotypes.
3. Spike at Your Service: Disregarding past continuity to make him incapable of doing the simplest jobs.
4. Equestria Games: Halfway through, he turns into an idiot.
5. Princess Spike: The quintessential awful Spike episode. Blatant contrivances, idiot!Spike, Spike's greed blamed for the problems when it's a non sequitur, and an ending with major sexist implications. If there was an episode where I'd say the show jumped the shark, this was it.
   

But ever since Princess Spike, his characterization significantly improved in a few ways:

1. Characterization consistency. There's been one or two episodes where he was hit with the buttmonkey status, notably in Newbie Dash as the tertiary comic relief. Other than that, there's been way more effort into giving him the treatment he deserves. Amending Fences and The Cutie Re-Mark in season five are two obvious examples. But season six is the most obvious. I'll get to that point in a bit.
2. He actually feels like a character. The Mane Six are all very likable, well-rounded, believable, and relatable. Unfortunately, Spike was the odd one out with the most inconsistency of the seven (now eight with Starlight). Today, his best qualities are not only brought to the forefront. Now he has flaws that make sense. It's like they take the best of Spike (A Dog & Pony Show, Lesson Zero, Dragon Quest, EQG1 & RR, Simple Ways, and Castle Sweet Castle) and develop him through there.
3. The roles given to him feel like he belongs. He spoke not much in Amending Fences, but he has reason to be there, and his role in giving Moondancer the picture in the frame brought that hanging plot closure. In The Crystalling, he and Starlight began a really good friendship; they understand each other and want to make things right. Spike wants to fulfill Twilight's mission of Starlight understanding the Magic of Friendship, while Starlight wants to patch things up with Sunburst. In the end, they figure out their way of solving her friendship problem.
    
   But then come his two episodes, Gauntlet of Fire and The Times They Are a Changeling.
    
   GoF reopened a hanging plot from DQ, and Lewis and Songco provided some level of closure. Not all dragons are sexist bullies. He regains respect for his race and understands them more. Ember is an excellent character. By winning the gauntlet and passing the scepter to Ember, he gains an ally in the Dragon Kingdom. It's his best strengths-focused characterization.
    
   Times gives us his most balanced characterization yet: flawed and prone to making mistakes without making him OOC, very responsible, and willing to sacrifice his reputation to do what he believes is right. Him befriending a race with a notorious history is something he can relate to. Thorax wants to understand the Magic of Friendship, and Spike bridges the gap to help him. Character development from past episodes sticks, and both episodes are for the better. This is his Wonderbolts Academy. Here's my mini-review for it.
   

I don't have any idea why that's the case. I have two theories:

1. Complaints of his characterization in seasons three and four impacts the rest of season five and this season. As written before, his low-quality episodes have always been a very sore spot for FIM. Following Equestria Games (which was sharply criticized for many reasons, one being Spike's characterization), DHX went back to take a look at what they can do better for him. Unfortunately, Princess Spike was too far in development to make changes, but they seem like they realize they can write him better. Since PS, DHX has put more and more effort into his character, and my theory is the criticisms helped give Spike some much-needed direction.
2. Josh Haber becomes the editor for season six: Aside from McCarthy, he gets Spike. He writes Spike better than almost anyone on the team, and him being there gives the writers a direction for the little dragon. Haber becoming the editor might be the best thing to happen to Spike.
   

Regardless how you feel about season six, there's one thing it does so well: Spike is getting the treatment he rightfully deserves. I don't know if DHX'll return to their old habits, but if they continue this current treatment, it'll be easily his best season yet.