Unlike the original Prototype, I find the challenges in Prototype 2 to be less frustrating and more challenging. This probably has to do with the goals for achieving a platinum ranking not being as outrageous as in the original game.
Something else that definitely helps is the fact that your score in each challenge is compared to a list of 10 additional scores achieved by other players, which really spurs me to try and place myself at the very top for each challenge.
I am pretty sure that the list of scores is not global, seeing how I always seem to be able to do just that, and knowing full well that I am not the best Prototype 2 player out there (nor am I the one with the most spare time). Also, the list of scores for each challenge, at least for me, usually contains the same names, albeit at varying spots on the list. I was wondering just who do these scores I am ranked against belong to? Players in my area? Something else?