Sonic: Plays like he does in the Adventure games, runs, spin dashes, home attacks, etc. He gets the boost later in the game after getting a pair of special shoes. You can switch between boost and spin dash whenever you want in the options menu.
Tails: Plays like Sonic, but can fly, and use ring bombs or his tails attack. He has occasional Tornado levels, were he can transport Sonic continent, but actually has CONTROL of the plane, and have lock-on capabilities.
Knuckles: Probably the most wanted replacement for the Werehog. He runs around in stages, beating the crap out of Dark Gaia enemies and Eggman's robots at night. He also has some of the treasure hunting elements from the Sonic Adventure games, and can collect upgrades and solve puzzles in his levels.
Amy: Plays similar to Sonic Adventure, but this time around can use the homing attack similar to that in Adventure 2's multiplayer, and Sonic Heroes. She can swing her hammer on the ground to destroy enemies.
Super Sonic: After collecting all the Chaos Emeralds, and beating Perfect Dark Gaia, you can play as Super Sonic in normal levels. He has an unlimited boost, and can fly around the stages. He loses rings at a rate of one second.
So... what do you guys think? :D