One of the most engrossing plots ever conceived in a video game.
It feels sort of dated, but for a game that's almost nine years old it's aged remarkably well.
I'm also appalled that some of you seem to have never played through it, lol.
I *still* play it every once in awhile, and the immersive atmosphere of the game still surpasses most modern titles imo, even though the mechanics of the game are a little out of date. It uses the old Unreal engine, I think.
If you haven't played it, I would describe it as a sort of a shooter/rpg in the same vein as STALKER: Shadows of Chernobyl, plus a crazy da Vinci Code style conspiracy plot that gets you hooked faster than crack.
Do yourself a favor and dl it. It's like $10 on steam, or you can acquire it elsewhere if you're too cheap.