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.
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)
It's on Q3 not on Q2 engine. Requirements are bigger than Q3 but game looks worst. Weapons are very badly made, that makes gameplay for kids +5 only. Tested on Windows and Linux - on both systems game is unstable. Easy to cheat and 80% of things mentioned in the reviews doesn't work at all.