For those hating this game for its difficulty or whatever, I completely understand where you're getting at, the game does get frustrating at some points, but if you stick to it and use smart tactics against certain enemies you'll be pleasantly surprised.
Also, the "easy" difficulty setting is there for a reason. The only achievement you'll get from difficulty alone is if you beat it on hard (which you have to unlock in the first place) so just play it on easy.
Leveling up and unlocking new abilities is a must in this game. You need to use your skills wisely against the right enemies. I personally loved this game because it gets so hectic. Everything is trying to kill you, the military, the infected, etc etc and you're a badass killing machine. This game really makes you feel powerful beyond measure, and it's gory as hell which I loved.
And to the guy that commented on its "PS2 graphics", really guy? The game looks pretty damn good for all the random action going on screen at the same time. Frame rate is very smooth and I think it looks just fine. Overall the gameplay more than makes up for graphics and if that's your reason for holding out on a game, I feel pretty sorry for you.
Prototype 2 looks like it improved the graphics though for anyone wondering. New engine and all.. I bought Prototype brand new when it first came out at 60$ and I still play it occasionally for fun. It's a great game to just mess around in after you beat it. Definitely worth 15$ for those that are at all interested. For those that came in here to bash the game, there's no need for that. If you don't like the game you're welcome to your opinion, why try to put off other people from playing it?