Red Orchestra 2 - Not sure if it is any good, but Install it and it is yours to keep.
It is a good game. Goes for realism, you don't get a magazine ammo counter but instead it just tells you "the magazine feels heavy" or "the magazine feels light", so you have a rough idea whether the mag you're putting in is still full or only has a few rounds in it
Cool game.
its only free till april 24th 10am