FPS's are a dime a dozen, well publicized and if they are over a year old now, chances are they are gettable under $20.
If anything, I'd say if you haven't played it yet, try Bioshock (the original), simply one of the best games ever.
If you haven't tried the series yet, get Yakuza 3 for cheap, which you could then check out Yakuza 4. I avoided this series for so long thinking it to be some kind of Japan centric weak GTA clone, but boy O boy was I wrong on that. Games are nothing like GTA (you never even kill a person the entire game), and there is enough gameplay to keep someone going to 50+ hours- one of the best values for the money