Alien Arena is an open sourced game that combines a sci-fi atmosphere with the tournament style deathmatch of Q3A and UT2k4. Major graphical features such as GLSL per-pixel lighting, ragdoll physics, light blooms, real time lights and shadows, textured particles, shaders, and reflective water, create a colorful and immersive deathmatch atmosphere. The game also includes mutators, adjustable effects, bot skill settings, and fully configurable deathmatch, team deathmatch, CTF, All Out Assault, Team Core Assault, Cattle Prod, and Deathball games. The game features original artwork, with a dark, sinister atmosphere combined with an off-the-wall campiness, and trippy, techno type music. There are currently over 60 maps, loaded with weapons(each having an alternate firing mode) and powerups. Alien Arena has fast, smooth gameplay, & players can play online against one another or against the bots. Please post all support issues in the forums for the game.
I remember installing alien arena 2004 when it came out... I had a wonderful time playing that(mainly because i had no games, and i had a really bad computer), but although it has improved A LOT, it's just too cheesy for 2011. But just like any game, there's no way it can stay in shape for over 7 years. Too many graphical effects; not enough graphical beauty, and an old(classic, call it what you will) gameplay style that adds absolutely nothing new to gaming. That said, it's a really nice free game, but i bet people would rather play Quake games than a Quake clon.
Competent, I guess, but the graphics are pretty bad and the pickup flashes are siezure-inducing. Humour is the one redeeming feature, but even that is a bit meh.
If you want an open-source free quake-like game, I'd heavily recommend Warsow (if you like the mobility aspect of it) or Xonotic (if you like the run'n'gun aspect)