This is one of those games capable of elevating the video game medium from entertainment to art.
First of all, the control system is terrible. Walking and looking are often awkward activities that really take some getting used to. Also, some of the minigames are downright tedious. For example, there's a scene in which your character is challenged to a game of basketball. You control your character through a very simplistic rhythm game scheme in which you push arrow keys and keys on the numeric keypad corresponding to what you see on screen. This is amusing at first, but you are forced to sit through ten rounds of this, which can take close to ten minutes. Not only does this get extremely boring and tedious, but it greatly distracts the player from the "meat and potatoes" portion of the game.
Also, some of the gameplay mechanics in action sequences are very poorly implemented, and you'll find yourself playing a rhythm game for 10 minutes to climb a couple of fences and ladders.
Another gameplay complaint is the lack of ability to bypass some cutscenes or sequences. At one point in the game, having to replay a certain section will result in having to listen to the same 2-3 minutes of dialog over and over again.
The story is brilliant, though it does seem as though the developers tried a bit to hard to cram surprises into the latter portions of the game. However, the story is still outstanding, one of the most suspenseful I've played (or read for that matter!) You will be totally drawn in and will be excited to find out what happens next. As I have already mentioned, the game/story draws significantly on previous literary, philosophical, and religious works to create a vividly artistic game experience. If you are a philosophy or literature buff, you will be especially pleased by this game.
Graphically, the game looks very good, especially considering its age now. Many of the performances were motion captured so they look great, and the environments, though small, are very thoroughly designed and detailed and immersive.
The audio is great, including an (at times) appropriately minimalist soundtrack reminiscent of Philip Glass and a talented cast of actors and actresses. A nice array of ambient sounds enhance the overall atmosphere of the game and contribute to the immersion felt by the player.
In summary, while the gameplay system is broken in many regards, the story is what really counts here. It is obvious that the developers of this game really believed that what they were working on was a piece of art, which fortunately shows through at almost every turn. If for no other reason, you should buy this game just to encourage developers to come out with similarly artistic titles in the future.