Here's what I gathered from the trailer.
First of all, it's a game in development. Those character models are likely to change.
Looks like it's a mix of Sonic Adventure and Sonic Heroes game play.
Sonic levels are classic Sonic.
Knuckles climbs and digs around looking for stuff.
Tails levels look like they'll play similar to Sonic Adventure 2.
Amy levels look kind of Prince of Persia-like.
Some levels they'll all run together like in Heroes.