Linux-gamers.net has posted a thorough, although harsh, comparison of free software shooters. It compares seven open source shooter games in a lengthy discussion. Few have gone to the trouble of comparing and carefully examining the genre before. The author ranks the games in the following order (best to worst): Warsow, Tremulous, World of Padman, Nexuiz, Alien Arena, OpenArena, and Sauerbraten. In making these choices, it claims to use gameplay, design, innovation and presentation as criteria and includes a short history of free software shooters in the introduction.

http://www.linux-gamers.net/smartsection.item.81/comparison-of-free-software-shooters.html