The season 6 Chang episode where he becomes super famous and they try to shoot a movie with him as the star without him actually being there was awesome. Other than that, I felt like they didn't know what to do with him after the first few seasons.
I'm surprised people didn't like that episode. Probably one of the funnier straight-up comedy episodes of the series, with my favorite Leonard line in the entire show.
But yeah, a lot of characters become "flanderized" which leads to funnier moments, but kinda bizarre to see where their characters end up.
Like, yeah, I couldn't stand Britta in season 1, but she is a completely different character by middle of Season 2 onwards. Which I preferred, but still off-putting.
I'd say
Jeff, Abed, Troy, Annie, and especially Dean Pelton all became better characters.
Pierce and especially Chang became worse.
Britta is confusing
Shirley was always my least favorite character.