for recent series I enjoyed more than I thought, bunny girl sempai and rent-a-girlfriend.
For just straight up subverting expectations I'd say anohana, and gleipner a little bit.
But its' an odd comparison because one happens in the beginning while the other is near the end.
Yu-Gi-Oh GX.
GX is different in that once it hits season 3 it changes. A lot. And this is important, because GX a lot of the time really isn't good, like, I'd say the first season of the show is bearable and the second is slightly more bearable, but the third season is really where it takes off. And it's not that unusual for shows to get dark arcs or anything, I mean this is YGO we're talking about but like...holy shit. A lot of the time this arc isn't happy in the slightest, like there's no real chilling out in the schoolyard going on. Just a bunch of losses and dealing with those losses and even the victories end up being losses, and it's not good just because it's dark, though I think that it realizes it can be what it is so effectively because of where the show was beforehand is a real strength. It's a really fun watch and the conclusion is surprising as hell.
Then there's the fourth season which is the best season. Of Yugioh. Period. Because while there is a big bad, he doesn't come until near the even despite that it's clear that the point of the season is to be a sendoff. So you get all these really just...nice character focused episodes that would contain all of these characters peaking in their character arcs and seeing how far they've come and it's just really, really nice. Especially in the case of Manjoume Sanda/Chazz Princeton who I'd write about but he deserves an entire book. Of the Kaiba expies he's the best by far and definitely the best character in GX.
So yeah it's one of the only cases I've seen of a show being only decently watchable, arguably not watchable for a good deal of it's run time and then just having this upward slope of really, really fucking good.
Facts, that show was a sleeper, but it got Really good by the end. And I agree the contrasting goofiness of the early seasons, somewhat made the rest standout even better, just because it made for good character development.
And I love Chazz too, but my guy was the little blue haired dude, he grew so much and became a badass in his own right.
It's easy to forget but that show may possibly be one the best examples of quality character development I have ever seen.
Even the side character grew as people, and went through moral or ethical reevaluations it was crazy.
I'd find myself rooting for characters I previously hated. But there were just multiple good "cartoon" shows airing around that time
There was that, Code Lyoko, Oban Star Racers. All extremely solid shows with great character development/change. Oban is my absolute favorite though.
Oh, Mairimashita! Iruma-kun. I never thought I'd enjoy that show, but damn if I didn't love every character, and wish there was a season 2.