After actually playing the game through multiple times, I have come to say this is easily one of my favorite games of all time. Is it perfect? No. Is it flawed? Yes. But honestly I do not care. Even in 2021, I still find this game, at least the original Dreamcast version, to be insanely fun.
Sonic's levels are well designed and a blast to play. Tails levels are more or less the same as Sonic for me, very fun to play through and speedrun. Knuckles' stages, while not perfect, are still really well laid out and the mechanics were intuitive, especially at the time. And E102 Gamma's stages aren't amazing but are really fun to just run and gun through. Amy and Big's stages still suck tho, however there's still a little bit of fun to be had even in the worst sections.
Overall this game is an easy 10/10 for me, however, it may not be for you, and that's completely okay. I'll still leave my old review up so you can see how my opinions changed.
Old review:
I don't really love this game, but don't hate it. I found the Sonic, Tails, and Knuckles portions to be fine, but Amy's gameplay sucked, and I haven't tried Bigs or E-102 Gamma's levels yet. This game is pretty flawed in my opinion, but there is still some fun to had here. Plus it has a good soundtrack. Just listen to "Open Your Heart," the games main theme. While it's not amazing, as it stands, this game is a solid 5/10 for me.