Sidrial is a computer game that serves as an expansion of Quake 3 Arena. This expansion is a total conversion, heavily tweaking the original game to merge the gameplay and cinematic aspects of the storyline in one program. In this game, a race is trying to destroy all planets with life forms, Earth included. Sidrial serves as the final outpost between Earth and the destruction of the latter. The game starts with the player's character escaping a prison. However, there are no other living humans in this particular prison. To escape, the player has to explore the said location, evade traps, and overcome various enemies and obstacles.
Similar to Quake III Arena, players fight on a number of maps filled with enemies that must be eliminated for those remaining to emerge as the victors. A number of weapons can be used. Every weapon is designed to be effective in some situations while relatively ineffective in others. These weapons are kept in the player's inventory. Dying in the game makes the player lose all his weapons. These weapons are dropped, at which point they can then be picked up by other players or computer-controlled characters in the game. This game, as is the original game it stems from, is played from a first-person point of view.