Ugh, I hate to say that I've given up on Sonic 3-D as a whole since Sonic Adventure 2: Battle.
It's a shame. I absolutely loved the original Sonic Adventure, every last bit of it, even more than the original Genesis games. I always thought Chaos was the coolest boss, and while losing the emeralds to Robotnik after working to find them was really annoying and predictable after the first time, I still had a lot of fun. Oh and the chaos could be addicting, too.
But then SA2:B had similar design, except without character choice. When playing the story, I could only choose light or dark, and not which specific character I wanted to play, which really hurt the game IMO. Each character had a distinct style of play, and if I was in the mood to fly down levels, I'd play as sonic; if I wanted to go hunting, I'd play as Knuckles. In 2 I was forced into those levels. (Not too mention I liked the way they pulled off the story in the original, even if it meant seeing the same scenes an extra time or two.)
I think from there, when they stopped giving people choice, was when the franchise started going downhill. Shadow, Sonic Heroes.. I just lost respect for them. Oh, and my friends tried playing through Sonic the Hedgehog 2006 or w/e over the summer.. it was a very masochistic experience.
The handheld 2d sonics (Sonic Rush at least) have been great - it's just the 3D ones that are going crazy! If Sonic Team would just make a 3d sonic game like Sonic Adventure or even SA2:B, I would pick it up in no time.