Overall impression : Rather good, but still needs work (I'll give them the benefit of the doubt, though, especially if the rumour about it being the TGS 2005 demo are true).
Sonic now excelerates more realistically (a contrast to the "Ice cube shoes on cling-film" control of Heroes and Shadow) . The homing attack seems more controlled now as well (if a litlle cumbersome, though). The main problem I had with it was the attack button, while pressing the X button sometimes would make Sonic perform his break dance esque Kick attack (ala Battle), other times it would send him hurtling of a cliff with no warning. Also, when attacked, Sonic no longer falls backwards, your still in full control, the only indication you have that you have lost rings is the sound effect and the flashing (which are both rather hard to notice in the heat of battle).
All in all though, it was still rather fun (yay for proper alternate routes, unlike the crappy fake diversions of Heroes). Nothing that can't (and hopefully, will) be fixed.