That's a hard question to answer.
For single player campaign, Ratchet and Clank: Tools of Destruction.
For single player quickplay, Guitar Hero 3.
For online multiplayer, it really is hard to beat Call of Duty 4: Modern Warfare. Far better than CoD 5.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.