I’m not sure what happened to Sonic Riders, but Sonic is getting an original title on the PSP entitled “Sonic Rivals”.
With single-player and wireless multiplayer modes, Sonic Rivals returns to classic 2D gameplay set in 3D environments. What starts as a friendly competition between Sonic and Knuckles quickly intensifies as Shadow and other rivals jump into the action, resulting in an all-out rodent battle royale. Players will negotiate wildly twisting 3D tracks while avoiding Dr. Eggman and his myriad of hazards, traps, and contraptions.
You be the judge. Links below contains a little bit more info and some screenshots.
Source: IGN: Sonic Rivals