Both me and Jamie have it with his working flawless while mine has sound issues (not that much of a bother as turning up fixes it but anything else on besides the game will make me go deaf) and crashes. Many people seem to have these problems but many don't either.
Without spoilers
Your this guy called Alex Mercer (did I spell his last name right?) you seem to be infected with some kind of virus and you can basically as you upgrade do all these great moves and you fight both humans and infected. It has free-roam and a lot of powers to choose from. You can also stealth with disguises

I understand it runs better on PC then GTA4 from what I heard. But if this is a good thing I do not know. I would prefer to get this game on xbox 360 to avoid these issues but right now I have it on PC and apart from the crashes I am enjoying it.