I just got it as Steam has it on sale at the moment, thought I'd pick up a bargain. Bitterly disappointed so far although I haven't been on the multi-player yet. The single player campaign has poor voice acting, poor script and I just can't get into the story. Maybe it's ok if you just want to shoot stuff but there are better games out there.
It may work for some people but for me it just seems cheap and nasty. Single player mode leaves you feeling so restricted it's just not fun as you can't seem to do **** until the game is ready, that includes walking through an open doorway. This video pretty sums up my experience of the game, fingers crossed the multi-player is better