I finished this myself yesterday. I'm always on the lookout for a good single player game and this one delivered. The campaign was a little on the short side but the story really drew me in and while I was expecting a few twists at the end, it still managed to surprise me somewhat. Unlike most games, the voicework here is top notch (you can really hear how the characters become more desperate and unhinged as the game progresses) and I give the game kudos for playing with your ethics; you no sooner hear your character say that you won't kill civilians only to be put into a position where you may have to do just that. The game is full of those kinds of morally ambiguous dilemmas and its a shame that the endings don't full reflect what actions you take.
Not much replay value (unless you want to mine for achievements and see the different endings) but definitely worth a playthru in my opinion. Definitely not for the younger set however,