I try to avoid becoming OP by giving my characters a truly fatal weakness. My amputee soldier in the other RP? He has no offense talents. NONE. The only remotely offensive thing he can do is teleport. Given the fact that he was a Ranger, this could make for some serious ass-wooping attacks, but the enemies our characters have to fight are the definition of OP. First few posts, one character has his face ripped off. 

HIS FACE. RIPPED. OFF. Another person got impaled by a javelin of ice.