I still kinda think Mercer from Prototype is overpowered. Maybe not within the confines of the game, but think about it. He's literally a mix of Green Lantern(can create things out of nothing) and Deadpool(is pretty much immortal--survived a nuke lol). He can somewhat fly, run on any surface, can cover himself in a full body armor that is nearly indestructible, can turn his arms into anything he can think of, can infect entire cities with his virus, etc.