I've played splinter cell chaos teory with a gamepad, but as you may know its more stealth and strategy based than fps :(

Half-Life 2 low req and it is Good (not whole with zombies but it still has a lot of 'em) u could also try Half-Life 2 episode 2 it has a lot of aliens and zombies, and there's still half-life 1 and its expansions, but it hasn't got the effects like hl2. all games named will run dreamy on your machine :)