This game has atmosphere that has yet to be matched in any other game I've played. From beginning to end, you're exploring a world that is cold, dirty, and depressing.
While the gameplay isn't perfect (the biggest flaw, I think, is the amount of back-tracking you have to do), it is a near perfect balance between twitch skill, creative tactics, and following clues. This is not a game for people who need their hands held by waypoint indicators. You need to move carefully everywhere you go, and save often - because you WILL die often.
The graphics, I feel, hold up pretty well. Textures are detailed. The level of gore is entertaining.
The sound is also very atmospheric, and at times ground shaking. When you step on a mine, or get attacked by an exploding dog, or get shot by a tank, you feel it.