I'm gonna get crucified for saying this...
I'm one of those sonic fans that had NEVER touched a sonic game until frontiers dropped. That was literally my first ever sonic game,so maybe that's why it's gonna affect my opinion so much, but...
Shadow Generations > Sonic Generations.
It's probably the controls or something, but I have much more fun doing Shadow Generations instead ot the original game. Now, don't get me wrong, I know that this game means a lot to everyone and all that, and I rewatched the original cutscenes probably a million times when I was younger, but now that I'm actually playing the game, I just like the more open world aspects that Sonic Team is going for instead. And I'm pretty sure this isn't even an hot take at this point, but Shadow's story is way better than Sonic's. Damn near felt depressed at the ending. Also the bosses are just way better.