This is one of the titles available in the Steam for Linux release. If you already have a license for it (I've owned the Windows version for about four years) it is already in your games list. At the moment it's $5, still looks great, and if you're willing to persist with initial slightly clunky feel you're in for one of the most enjoyable and atmospheric online FPS shooters ever made. Hopefully Tripwire will also integrate Darkest Hour, which is a superb mod that features the Western Front.
The pace is somewhat slower than most shooters, and teamwork is naturally encouraged. Once you're used to the mechanics it's very rewarding, and never dull.
Some Linux gotchas:
Switch scope options to 'textured' in display options, on some configurations you cannot see through it without setting this.
Toggle 'Motion Blur' as it can cause some problems with certain game objects, try it and see.
Widescreen support: Change the entries in ~/.redorchestra/System/RedOrchestra.ini under 'FullscreenViewportX=[resolution]'.
FullscreenViewportY=[resolution]' Most game options can be changed from this file, including those greyed out in the gui of the Linux version.
Outside of the above, I've had no issues on Arch at all; it's been rock solid.
Some screens from the Linux version from various online games I've played:
A distant Tiger tank (yes, there are tanks, yes, you can crew them) that was an absolute menace during this match:
The bloody assault on the rail yard at Stalingrad:
The sewers and streets of Leningrad, 1941:
It's 2006 vintage, so should work well on older hardware; I've got an Nvidia GPU but have not tried other configurations. My steam user ID is the same as here, if anyone wants to add me.