DeusEx

DeusEx (Eidos / Ion Storm, 2000) is a FPS/RPG for PC and PS2 set in a cyberpunk world, decaying under the rule of rogue elements of the Illuminatti and various other conspiracy-theory favorites. Nanotech and cybernetics are just coming into military use and you play as the 2nd ever nano-augmented agent for the United Nations Anti-Terrorist Coalition. Through the course of the game, the main character has several missions in New York, Hong Kong, Paris, Vandenburg, an underwater lab, and of course, Area 51.

It's the first FPS that I've seen that actually had a decent storyline, and also one of the first that actually allowed the player to choose what to do. Almost every objective can be completed in at least a few ways from sneaking to brute force (weapons range from tranquilizer darts to nanotech swords to flamethrowers). I think it's a contender for best game, but that might just be me. :P -AlexUtter

• Best Game Award, seconded by BrianKirkpatrick. The spectacular storyline alone makes it worth playing, but some of the graphical effects, which were quite good at the time, are still pretty fun to watch (the game was built from the Unreal engine, btw, and does some pretty cool things with what it was given). On the other hand, the demo alone was enough to turn me off from the sequel, and having just seen the beginning movie the other day, I don't think I'm going to play it any time soon.

DeusEx 2 is also available, but not generally considered as good as the original.

See also: GameChallenge. This game is especially good for coming up with game challenges because of the sheer freedom of action that it allows.