Was a game that came out in 2000 and many people don't like it. Not because it sucks but because it set the bar way too high and nothing else has been able to match it. It is, IMO, the best game ever.
Basically it's The Matrix meets 1984. You play as a special nano-augmented agent trying to uncover a conspiracy. The game progresses based on your choices wether or not to kill certain characters, tell people certain things, etc. It's basically a first person shooter mixed with an RPG. You can upgrade your weapons, gain XP, skill points, etc. Basically you can customize your character to suit your style of play. If you like open ended games and lots of deep sociological and phiolsophical overtones, then check it out. Read the wiki for more info.
A sequal was made called Invisible War that didn't live up to the first, mostly cause of stupid ideas (universal ammo, lacking plot, etc). A 3rd game is currently in the works, although Warren Spector isn't on the development team this time.
intro - http://www.youtube.com/watch?v=CbYTVfM4amc
one of the endings to the first game - http://www.youtube.com/watch?v=ye68o...eature=related
convo from 2nd game - http://www.youtube.com/watch?v=xBeoreJr4Yc
one of the endings to the second game - http://www.youtube.com/watch?v=zeboq...eature=related
trailer + info on the 3rd game - http://www.youtube.com/watch?v=fkXCE...eature=related