Mini-Review:
So, the game is actually quite good, and the one major fear I had was put to rest. You are certainly NOT overpowered and the game is not easy. The parkour game mechanic is almost unnaturally satisfactory. The combat is fair, and the story is decent. The amnesia thing actually works quite well because it all felt appropriately. Its like Mass Effect's story, Mass Effect did nothing new, but it approached the overused sci-fi genericness with such pizazz that I didn't begrudge it. Its the same way with Prototype. The story is quite overused but its done in such a wonderful way.
Alex Mercer seems to be the mutant son of a Wolverine, Spiderman, Nightcrawler, and Mystique, and its pulled off quite well. You have a nice illusion of power but not too much, you feel epic and powerful as you can sling cars at people, create little shockwaves when you slam into the ground, and the feeling of slamming huge rockfists into a tank until it blows up is quite satisfying. However the game still keeps a level of difficulty as there are mutant creatures and tanks who can take you down if you don't be careful.
Buy it, or at least rent it.