The Adventure games were just fine. Sure, they were glitchy, and the camera was a pain compared to other 3D games. But you know what? Those things just managed to get worse over time, that's the problem. They were moving in the wrong direction, it's not because of the dimension of the game. If they could get back to at least the polish of the Adventure games (better than that would be optimal, but let's be realistic here), and made sane choices (ie. no [tornado fang]ing werehog), then Sonic in 3D would be just fine. Now get your head out of your asses and think a little bit more.
Adventure and Adventure 2 were very focused in one direction (with a few walls), and between the Rail Grinding and those "On-Rails" segments, it provided a moderately satisfying experience akin to the 2D games. I use Emerald Coast as an example often not only because it is so close to the perfect 3D zone design in that it was not only simple enough and still focused on platforming and momentum/speed, but the atmosphere was absorbing and it had special segments like the whale, or the waterfall run, all sorts of moments.
But even then, Sonic Adventure 1 and 2 still had a few glitches, but they were blemishes on an otherwise decent game rather than further aggravations to an already poor experience.
See, even this I can't get behind. There are elements in tons of other games that tell me that momentum (and speed based rewards) can be applied to a 3D Sonic game without horribly breaking the gameplay. Jet Set Radio comes to mind almost instantaneously for a few of the race segments. Funnily enough though, there are two great examples of how Sonic can be done in 3D, and both are racing games, namely F-Zero GX & Trackmania (especially Trackmania).
I'll get more into it in a second though.
There's one thing to keep in mind about that. F-Zero GX, Trackmania, and Jet Set Radio, for the most part, are set on one line. And, unless you mess up, it's hard to "fall off" (unless we're talking about F-Zero's harder segments like the Creators' Race, then HOO BOY, GOOD LUCK).
Meanwhile, Sonic games are also open-bottom, shifting levels of position, and attempting puzzles. You can go the "racing" route, but then it gets boring. Sonic Rivals. Shadow's stages in Sonic Adventure 2. This would be remedied, however, if you did that design with the "shortest route" and reasonable-challenge based Time Attack unlocks of Sonic CD.