People nowadays think that Sonic games should be about blazing through the levels at incredible speeds.
Unless I was playing Bubsy, the original Sonic games were focused on platforming, Chemical Plant Zone being a great example of a stage that required good jumps. Sure, you could get through the earlier levels fast, but that was because each level had lots of different routes to the the end. I also miss the traditional level formula of Act 1, 2, then 3 and boss.
I am a fan of the 3D games, but apart from the character you play as, they bare no resemblance to Sonic whatsoever. I don't care for the story, and I never really had a problem with the controls and camera, except on a few certain occasions.
However, I don't like the fact that you only spend about 50% or less of the game playing as Sonic and running through levels, except for Sonic and the Secret Rings, but that only picked up at the later half of the game. Other characters are OK, as I enjoyed Tails' stages on SA, as they were similar to the stages Sonic plays, and I even liked certain missions of Amy. However, the shooting, collecting, fishing, driving and beat em up levels are unnecessary, and distract from the Sonic experience.
I don't think Sonic needs to go back to his 2D roots, as I found Sonic Advance 2, and Sonic Rush to be worse than the 3D games, but that may be my dislike of grind rails XD.
Sonic just needs to turn to a Sonic, and if that means trying to make a 3D game with the level format of the originals; without adventure stages and other character specific stages. Other playable characters would be cool, especially if they could go through different routes in the level.