Warning: Wikipedia contains spoilers!
Created by the designer of System Shock, Warren Spector, and built on the Unreal game engine, the game combined the action elements of a first-person shooter (FPS) with the character development interaction of a role playing game. The game, set in a near-future dystopia, featured environments often drawn from real locations and that seemed to more accurately depict real environments than other games to date. It was also notable for the complex tactical possibilities, where players could choose many different ways of achieving evolving goals, from stealth (akin to Thief) and long-range sniping, to all-out combat with various heavy weapons, to character interaction and use of objects in the environment.
The plot managed to draw together many current conspiracy theories into a narrative with characters that were deeper than those of most FPS games and presented a philosophical dilemma in the conclusion where the player must choose between courses which lead to the continuation of 20th-century style capitalism with all its flaws, returning the world to a dark age of medieval anarchy, or choose the peace offered by the benevolent dictatorship of an omnipotent computer.
The game was hailed by many critics and users as a significant step towards a "reality simulation", as one of the first games to truly pioneer the effect of moral choices, and one of the only games in existance based on violence to offer a non-violent alternative, killing is not a necessary part of Deus Ex. Some have complained however of technical flaws (the graphics were not state-of-the-art and the game ran slowly on machines not fitted with 3dfx video cards) and found the game too difficult to complete.
A sequel, Deus Ex: Invisible War, was released on December 3, 2003