From what I played at TGS, i liked the speed, but the 2 screens idea REALLY REALLY disrupts that speed. Its far too disorientating, and in some sections it just is plain awful.
The level I played was Blaze the Cat in the water level, which was pretty rubbish tbh. The Sonic in the green jungle zone level looked good, but as is Sonic Team tradition usually the first level is good and the rest is piss poor.
As for enemies, all you're getting are the enemies from Sonic Heroes again I'm afraid, other than the bosses.
I personally find this game disappointing.