. I consider Painkiller to be the best mindless slaughter game of them all though.
Painkiller's got my vouch here, haven't had so much fun playing an FPS in that genre style since Doom2. Now if only it had multi-player co-op....would love see'ing I & others team-up and pile-drive multiplaye waves of monsters into the walls with that wooden-stake-gun thing at the same time.
Anyhow, onto topic, my bro has Quake4 here (DVD edition, since he also wanted the Quake2 expansions included with it, which we could never find back in the days), and from what I've played from it, it's just a better Doom3 single-player game (which I only ever played just for the atmospheric setting/graphics, the shooting was lame to me, never enough targets at once to fire at) with a rehashed online gameplay system from Quake3 iirc.