Thanks to the division of developer Ion Storm into two separate entities (the other being responsible for the collosal failure of Daikatana), Warren Spector's Deus Ex was a revelation in gaming when it came out in 2000. A story of a criminal consipiracy working in the background to usurp the United States ran alongside the development of AI, nanotechnology and human augmentation, with you playing a genetically and nano-augmented super agent of a government agency.
Thrust into a game world with plenty of backstory to discover, plot twists and lots of great touches everywhere, Deus Ex needs an entry in my Saturday Soundtracks list. The UNATCO HQ theme is a great standout track, as it is one area during the beginning of the game that you repeatedly come back to and it works well to describe the humdrum office environment and some kind of resemblance to "home" during the game.
Technologically speaking, the game is based on the venerable the Unreal Engine, something that up until this point had just been used for "mindless" first-person shooting games. Like Half Life, a game that had been able to run on lots of older machines because of its reliance on a modified Quake engine, Deus Ex brought a familiar game engine to the fore and then updated and tweaked every aspect of it to suit their game. In particular, the game is famous for allowing lots of different approaches due to a limited inventory and non-lethal approaches, with a set of skill tree that allows you to customise your character exactly as you see fit. For its time, and still now, it was a brilliant example of emergent gameplay, with people finding ways to enjoy the game in terms of bending and breaking the laws of the game to suit.
Speaking of technology, the music in particular carries on from the tradition of Unreal Tournament, in that all tracks are sequenced on an old style tracker. The upshot of this is that the music was dynamic; stopping and getting more upbeat during the stealth missions if you were discovered or during quieter moments of the game during conversations. The soundtrack itself is spread over numerous areas and countries, with lots of variety and the use of the game's main theme as a leitmotif throughout seals the deal.
In particular, this track reminds me exactly of why the soundtrack works; set in the underground section of your familiar UNATCO base, you awake to find yourself captured with no weapons and have to find your brother, your gear and the way out. Discovery doesn't mean certain death, but with no way to fight or heal, you need to adopt a silent approach and the music definitely works to raise the tension.