4. Alex Mercer - Prototype
The "amnesiac science experiment hunts down creator" storyline has been overused, but never is such a versatile, player friendly manner. Where else can you eat a civilian, absorb his body and then run up a skyscraper in his skin, jump 200ft and then tentacle some soldiers and pulverize them? Shape-shifters are often portrayed as infiltrators and con-men but rarely do they use their abilities to create weaponry with their anatomy (an exception being the Sandman), and it really pays off in this sandbox adventure.