100% completed Sonic Generations last night.
Honestly, on a revisit... While I absolutely did greatly enjoy it 10 years ago, trying to play it to 100% changed my opinion of it significantly. Some of the mission gates were pretty miserable (admittedly, that's kind of on me for trying to S-rank absolutely everything even if it wasn't a regular Act) and Classic Sonic controlled significantly worse than I remember, especially the Spikes Wisp. I'm not a fan of the Rocket Wisp either, which Modern Sonic gets, but at least what little control there is to that one, I can manage just fine.
I do hope there's significant improvements to the Sonic side of the game in Sonic × Shadow Generations. Aside from what's shown in trailers and the Steam page, I don't really know what to expect from the Shadow side of the game, which is what all the marketing is pushing; not that I blame them, considering the Sonic side is all but guaranteed to just be stuff we already had 10 years ago with regular Sonic Generations. Nonetheless, I'm looking forward to the Shadow side of the game; he's my favorite character, and he draws mostly from Modern Sonic's gameplay, which I found I preferred not just here, but in Sonic Forces as well, where Shadow played almost exactly the same as Modern Sonic; in this new game, he's getting some new abilities, so he'll be set apart from Sonic in a way that'll be interesting IMO.
I dunno what it is about these anniversary games that bring Classic and Modern Sonic together, but for some reason Classic just doesn't seem to do well... His Spin Dash goes faster (in Generations at least) than it ever did in any actual Classic or Classic-styled Sonic game, which can be great for speedrunning, but there seems to be something fundamental about these games that makes him interact weird with the environment.