Prototype 2 is a big step up to the prequel in my opinion. The game has overall improved from combat to graphics. I've only played around 6 hours of the game but there is a large variety of things to do in a huge open world sandbox. The story is also interesting and the develepors have done well to tie it into the prequel.
Overall Prototype 2 is definitley worth the buy, I would recommend it to anyone who loves free roam and lots of action!