Got to try it, the way the game "feels" is much worse than I thought, especially for someone that plays the classics occasionally. Even after getting used to it, I still don't like how it feels, Sonic kinda feels too "heavy", and then there's the physics (spinning being slow, losing momentum while not pressing the directional button).
The game is not too bad, but it's not a worthy sequel to Sonic 3 & Knuckles. My personal score is somewhere around the 5 to 6 range (in a 0 to 10 scale).
It might sound that some of us are being a bit too harsh with the game, but imagine if SEGA made a sequel to the Adventure series, Sonic Adventure 3, and in the end it played like Sonic Unleashed Wii without the boost. It wouldn't be a bad game, but it's something the Adventure fans wouldn't be happy with.