There are 2 new characters, Shadow and Rouge. Shadow is a Sonic parody with jet roller blades and Rouge is a female undercover, master Emerald stealing bat. It's an extremly easy game, even more so then the first one. It does have replay value but not a whole lot. The Super Sonic/ Hyper Shadow bit is easier then Sonic Adventure 1 because although you run out of rings you don't have to collect some that will never come back and hope you finish it off before you run out completly.
This is also the first ever game you can actually play as Robotnik, even though it sounds like a good idea it sounds pointless because you don't get to play in any of his well good machines, just a walking bot.