In the fractious future of Gamer, videogames have ''gone human,'' with real live blood-sport warriors controlled by geeks with joysticks. The sickest of these games is Slayers, in which death-row inmates kill each other off in a noisy orgy of skip-stutter editing and dirty-ash-spattered explosions. It's The Dirty Dozen meets TRON, updated for the age of action incoherence. As the brutish Kable, Gerard Butler must find out who's pulling his strings, but it's the audience whose chain gets yanked by this headache-inducing techno-violent mishmash.