Violent or gore?
Violent hmmm, are we all Xenophobic? (means hate foreign things, ie aliens, kamie's and zombies)
If we are keeping it to human on human violence then I would say probably those games, if it's just violence, then I would have to say either Unreal (nothing quite like multiple rockets to the face of the unsuspecting noob that's following and doesn't think you noticed), Doom3 (daemons are lifeforms too, lol), Quake4 (main character gets sliced up and butchered to make him half alien cyborg), or say something like Halo (Halo series is awesome only because you can beat down the aliens, you could shoot them since space invaders, however when I get pissed playing, it's so awesome to actually beat down a red elite on heroic, that or stick them hehehe.)