Sonic the Hedgehog has never seemed complete. While Sonic the Hedgehog can be great on a good day, it can also seem old, tired, and redundant if not in the mood. It is this, perhaps, which is why it seems Sega feeds it's critics, yet also feeds it's fans with what they know they want. It's hard to balance nostalgia and state of the art. The reason that Sonic worked in the first place wasn't because it was deep. In much the same way RoboCop worked, Sonic the Hedgehog was just per gritty fun, and when it was over, you didn't care, but you came back to it again and again.
Sonic the Hedgehog came about at a time when the Genesis needed something to battle the Super NES, and like a miracle from God, Sega pulled out both their first mega blockbuster game, and a mascot! Sonic the Hedgehog was not better than the best of Super Mario Brothers (the closest competition, outside of Bonk on the TurboGrafx), however, Sonic the Hedgehog was up against a weak offering in the Mario Saga (Super Mario World on the Super NES). And Sega proved to be edgy by pulling out a kick ass ad campaign that both lambasted Nintendo, and yet seemed completely cival. Even later rip offs by Sony and even Nintendo seem forced, and never quite seemed funny like Sega was funny.
So with all this, how can Sonic Adventures, which could be considered Sega's long awaited answer to Mario 64, live up to all this nostalgia? Simple, it can't. But Sonic Adventures isn't have bad, either. The inherit problem from the get go is that it took Sega nearly four years to answer Nintendo's Mario upgrade, and now, with no major improvements in place, Sonic Adventure just seems gimmicky.
It's not without merit, though. The graphics are stunning, even now they come off nice and crisp. It's hard to go back to Mario 64 after playing this, even though this game isn't nearly as deep. The variety of different graphics are nice, but what makes Sonic Adventures shine is the attention to classic levels. Intact are the Sonic Spinball levels, the speeding snow levels, and many more. Each brought to life in mostly-full 3D, and all too fast to catch all the detail.
The music on the other hand is horrible. It's almost worth not mentioning at all. It was one of the few games that had me reaching for my audio cassettes of the New Kids on the Block.
The control is tight, a lot tighter than I had original envisioned. However, it should be noted that while you always know where you are going, a lot of the game (perhaps too much of the game) is spent simply holding the direction you were holding before Sonic started running. Sometimes it seems like when Sonic starts running it's almost like a mini cut sequence. These scenes do indeed give a good sense of speed and always make a jaw drop if you haven't seen the game before. But it seems like there are too many of these sequences, and it quickly diminishes the replay.
The game has several other games built in, helping ease criticism like what you read above. You can play as Tails, Knuckles, and several other "secondary" characters based off of the Sonic cartoon, and Knuckles Chaotix (for the 32x). Some of the levels are the same as the Sonic adventure, however, other levels are completely different, or at least greatly different. All are somehow customized for the character. However, it's only when you're playing as somebody slower than Sonic that you really notice how shallow each of the levels really are. Since you are mostly speeding through the levels, Sega did not add a lot to each of the levels, so often times it feels like going through with another character is simply playing the same game, slower.
And to add salt on Sega's injury, Sega didn't even launch Sonic with a good add campaign. It's not that this game is awful, because it's highly recommended, however, it's far from perfect, and not even close to Ape Escape or Mario 64. Taken on it's own, however, Sonic Adventure shows much promise of what future 3D Sonic's bare to hold.