Really? I play for both reasons, for the skill involved AND the senseless killing. It can be SO therapeudic mowing through multitudes of zombies, demons, humans, bots, deers, mortals, Gods, Grizzly Bears, and anything else that gets in my way when I come home from a shitty day. Same thing for Street Fighter II and Mortal Kombat games... it feels so GOOD to beat the living shit out of Deejay with Blanka, after I've had my ass kicked by 999 with like five other characters, and at the same time, it took some skill (and I think he was playing nice) to beat him. It's also just too damn cool to see someones head explode in a fountain of pixelated, red blood, you can't argue that
