"Quake II, released on December 9, 1997, is a first-person shooter computer game developed by id Software and distributed by Activision.
Quake II takes place in a science fiction environment. In the single-player game, the player assumes the role of a Marine named Bitterman taking part in "Operation Alien Overlord", a desperate attempt to protect Earth from alien invasion by launching a counter-attack on the home planet of the hostile cybernetic Strogg civilization. Most of the other soldiers are captured or killed almost as soon as they enter the planet's atmosphere, so it falls upon the player to penetrate the Strogg capital city alone and ultimately to assassinate the Strogg leader, the Makron.
The game is played in general first-person shooter paradigms, in which the player shoots enemies from the perspective of the main character. The gameplay is very similar to that featured in Quake, in terms of movement and controls, although the player has been slowed down, and now has the ability to crouch."
Source: Wikipedia, "Quake II," available under the CC-BY-SA License.