Unreal Tournament 2004 demo
Full user review
Nice graphics, nice music, nice gameplay, tons of mods available (just look in filefront :P) Native Linux Installer.
It CAN make you get pissed off, if you ain't got a nice and decent computer... and if you fight against Xan or Malcolm. I beat them though :P
Really, after so many years, I still love this awesome game. I only wished I could find this game at a retail store. I heard you can buy it for roughly 9 bucks. Sigh...