Depends on what you like in shooters. The games you listed are all very different from each other, so I'll just present my opinion, which probably doesn't come as a huge surprise: Get Arma2. Any serious bugs are ironed out by now and as in previous games of the series the replayability value is off the charts with all the user-made content. Especially if you prefer multiplayer to singleplayer this is a clear winner, and it should run ok with mediumish settings on your rig. My second choice would be ETW, which I don't own yet but I've heard good things about it. I would forget about Crysis and instead spend the money on beer
