The best single player game I've ever played. Incredibly challenging (more so if you want all the upgrades and energy tanks). Puzzles will make you think and backtrack. The game is quite unforgiving to be honest. But once those gears in your head get turning, the creativity of the features, the level design, and the music combine to give you an unparalleled single player experience. Everybody who likes a combo between FPS and adventure, this is a dream.
