Killing Floor: Incursion
Beat a rampaging genetic monstrosity to death with his own arm. Then take his head and use it to throw at your next target. Or be totally unoriginal and use guns. The "massive evisceration and trauma" or MEAT system that made Tripwire's 2009 original PC shooter so fun is put to good use here, and the option to play co-op and wave at your partner over the corpses of your slain enemies is a special feeling. Also it turns out that hitting monsters with stuff is great cardio.