[Bozos of Bones]

Best Single Player FPS I've ever played. Why? Atmosphere, AI, realism, HL1 references, Big Brother...
If you just run and shoot, what is teh AI supposed to do? Shoot, what else. They duck behind cover to reload, they attack in teams, and the bastards are really precise on higher difficulties. If, on the other hand, you try to use some advanced tactics against the AI, then it really comes to shine. If they are set to hunt you, they will hunt, they will search and the will kill. What more do you want from an AI, to sit down and have a cup of coffee? The game is really all that.