The game's not boring or a buggy mess, but it doesn't do anything great either. The later stages introduce some interesting mechanics, but then the game ends. No one asked for Classic Sonic, and all stages are way too short to be memorable. Avatar creation is cool tho.
Classic Sonic is a bit of an meme but Modern Sonic goes hard, even though the stages are not as cinematic as the Unleashed ones they are a lot more diverse.
Modern stages are way too quick, but decent. Overworld is actually really fun. Not exactly what would be my dream game, but damn this one's good. God I wish sonic team just chooses one gameplay style and sticks to it for the next one.