Apparently the devs of Sonic Mania are making a new game called Rollin' Rascal. It's pretty much off-brand Sonic, but there's a demo available for the game and it's actually really fun.
I'm surprised Sonic is still around. I haven't played a good Sonic game since Sonic Adventure 2 (except Mania). Wasn't a fan of Shadow the Hedgehog, and never played some others I've heard were good like Herpes and Unleashed. Generations was alright.
There have been some generally well-received games since Adventure 2, like Generations, which you mentioned, along with Colors, Mania, and Frontiers seems to be generally liked enough.