If you pre-order Prototype 2 at Best Buy, you'll be getting your hands on the "Hardened Steel" bonus. From what I can tell, this bonus almost breaks the game by making Heller near-invincible whenever he gets into a military vehicle.
Just watch the video above, where Heller shrugs off everything that Blackwatch can throw at him. I am trying to decide if that's unbalanced, or simply the natural conclusion of a game that revolves around power fantasy. Who knows?