It's been a while since I posted a straight-up action game, so here you go: check out Ownage Burst. It's pretty much a mindless shooter, but there is a bit of strategy that you might pick up after a game or two. You can duck behind obstacles to patch yourself up, and you have a handful of (slowly respawning) grenades that can take out a group of enemies with a well placed throw. Also, it helps to aim for the head. Pew pew pew!