The PS2 and PSP versions are essentially identical. The only differences worth noting are the multiplayer races and skull challenges. The former play out like Mario Kart trapped in Hell and the latter put you inside each level with specific goals to achieve. Don't get hit, use your Penance Star this many times, stuff like that. Completion rewards you with skull tokens, which you use to unlock PSP goodies.
As if you needed us to tell you, Ghost Rider will be out in time for the movie's February 16 release. The game isn't going to change your life, or make you throw away all other action games up to this point, but anyone who likes stringing spiky punches together should eat this up. That goes double for comic fans.