Bit of a controversial take here, but I feel like Sonic's characterization has gotten more stale and generic. Back in the day, atleast outside of Japan I believe, wasn't he advertised as an edgier, spicier, Mario? I guess he still can be considered that, but that's comparable to being slightly spicier than water (which isn't saying much at all). I guess it's mostly a mixed bag throughout the series' continuity, but atleast in the earlier days he seemed to be more spunky and have much more of an attitude (his impatience for example being one of his most prominent traits). His most modern appearances have toned a lot of that spunk down, and have pushed more toward a mature, serious angle. And while that is fine in itself, removing those quirks and traits that made him unique and flavorful only downgrades any sort of 'mature' development he has. Fans love to go on about how character development is important, and it can be, (personally, while it can be important I do not think it is vital but that is a discussion for another time) however removing traits that intrinsically defined a character or made them interesting is not the way to go about it. A character's flaws are what brings life to them and does not resign their status to nothing beyond some sort of emblatic figure-head. True character development, is not absolving one of all their unlikeable flaws, but having them progress in spite of their flaws (and I'm only talking about 'positive' character development in this scenario).
And if I were to go even further, the 'hated' writing of the 2010's Sonic games, while not completely favorable, weren't as bad as people make them to be. It stayed true and honest to the light-hearted, comedic nature of Sonic. Again, Sonic isn't supposed to be some generic heroic persona, he's fundamentally a light-hearted person who has some personality traits that tend to get on other's nerves from time to time. He's prone to making jokes at other's expense, being too easygoing at times, again somewhat impatient, and also somewhat inconsiderate at times as well. When it comes to showing these 'problematic' traits of his, I think the 2010's games did well despite their criticisms. Sonic (the series) isn't supposed to be super serious all the time. Even a darker game like Sonic Adventure 2 had its lighthearted, funny, moments. (I would say Sonic X too but I'll try to keep it to game only discussion).
Sorry, I know this is somewhat off topic, but I was just thinking about the contrast of character between older and newer games. And while I have a bit of problem with Sonic in more recent titles, they hadn't desercrated him as much compared to other characters (Looking at you Amy). I don't know, people make jokes about how media literacy is really becoming less and less of a thing, but I honestly do feel that way. Characters' flaws aren't actually flaws (as in, beyond some silly gag moment they don't actually suffer in some way because of that flaw), a lot of characters' personalities are recessed so that people can project onto them, and if characters do have a controversial flaw that is considered quite 'problematic', many people with their black and white sense of morality see them as totally irredeemable. Many people forget that a 'good character' isn't always someone you necessarily agree with (or always agree with), or someone you look up to, or even someone you would personally like. Life is so much more nuanced than that.