Sonic Heroes was pretty much the start of the downfall for sonic games. Nevermind the fact that the controls were slippery & shitty as hell, but the characters defenitely did a complete 180. For example...
-Sonic is always cocky & in control... never surprised by not only the fact that Metal Sonic got more powerful, but also that Shadow was right in front of his face even though he saw him DIE in SA2
-Amy started her psychotic "ZOMG SONIC MARRY ME PLOX!!" attitude in this game, which got even more annoying in future games
The other characters have issues as well, but the point is, it's nothing worth checking out unless you're an avid sonic fan. Apparently from what I've heard, the Gamecube version is ok, and i have the PS2 version, so maybe thats why.
Also I'm really not a fan of the whole "team" thing... I liked it better when each character had their own adventure (Like Sonic Adventure 1 and Sonic Advanced 1)