Last I heard Tails wasn't going to be in this game (i think i read that on ign's article). If so, that is a real disappointment to me. Some of my best memories with the Sega Genesis were of teaming up as Sonic and tails with my little brother. Can't they do the same with this title? At least local co-op and even better if over Xbox Live.
I liked Sonic Adventure 1 and 2. Haven't played any others. If you can block out the grating voices, they're good games. Only thing I would've liked is better multiplayer modes.