Deus Ex is a 1st shooter, but plays like a mix of System Shock 2 and Thief, with a ingredient of Half-Life and Rogue Spear. There's an intricate skill and "nano-augmentation" system which lets upgrade your ability and body as the game goes on. Skills include things like lockpicking and rifle accuracy, while nano-augmentation affects things like strength and resistance to damage. In the game, you play J.C. Denton, an elite special agent working for the UN's counter-terrorist force, about 50 years in the future. The future is a dark and horrible place, according to Deus Ex. The world is ruled by powerful corporations, and shadowy government organizations. Terrorist groups run rampant, and a lethal virus is spreading slowly. To facilitate that replayability even more, Ion Storm is designing Deus Ex so that there are always multiple solutions to every problem. For example, if you play the game as a hack, you can use your computer skills to open a door. But if you're a weapons expert, you may want to try to blow it open instead. Visually, the world of Deus Ex is simply amazing. I haven't seen a game with an environment as interactive as Deus Ex's since Duke Nukem 3D. Just about everything is open to manipulation by you, right down to the drinking fountain that gives you health.Also talking to NPCs is a vital element of the game because they give you information about your mission or will give you weapons or different items to use. I can say that this is definitely one of the best game so far this year. If you liked System Shock i bet you will like this game either. Anyhow, before you'll run to buy Deus Ex I definitely recommend this demo (139.4MB).
Also don't forget to visit Deus Ex website for more details.