On http://www.linux-gamers.net/smartsection.item.81/comparison-of-free-software-shooters.html you can find a very nice comparison, which is pretty extensive and to my shame I have to admit that I haven't played many of them - I really ought to try War§ow soon.
Nexuiz gets a pretty good review (in your face, AlienArena 
) but still note:
While most of the game is cleaned up far beyond its Quake 1 roots, it is still lacking in presentation with the menu being very circa 1990s.
/me sighs
I officially suck...