Who says Ubuntu Linux is not for gamers?! Looking for the best, hottest games for you Ubuntu Linux computer? Check these games out!

Tremulous | Gridwars | VDrift
World of Padman | Nexuiz | Scorched 3D
Glest | Flight Gear | Battle for Wesnoth
RTCW Enemy Territory | Alien Arena 2007 | Action Cube

#1 Tremulous (tremulous.net)

A team based first person shooter (FPS). Tremulous is free to download and play.
In Tremulous there are two teams: Aliens and Humans. Aliens can have such awesome feats as wall-walking (dizzying to say the least), pouncing from great distances, and spraying poisonous gases. Humans can obtain advanced weaponry and armor, and plant strategic devices such as turrets to defend their base.
Tremulous features a unique upgrade system, where players from each team must make a certain number of kills to gain new upgrades (aliens can evolve into more powerful aliens, and humans can obtain better items and gear).

Install:

sudo apt-get install -y tremulous