Spec Ops: The Line
Oh wow, this really got to me! The little changes throughout the game as the guys slide downhill, from the one-liners the characters spout, to their increasingly blooded faces, to the way they execute nearly dead enemies. The story is pretty good although if the moral aspect is meant to feel shades of grey, I thought it was pretty black and white.
The mechanics are a little off, I died a few too many times because Walker didn't want to get into cover, and he seems to die a little too easily on Normal difficulty anyway.
Play for the story and character arc. Certainly not your typical meathead shooter. 9/10