For a game that I got free with the Orange Box expansion of Half Life 2, this game certainly did warrant my attention.
In the beginning the puzzles are almost mind numbing in their ease, but, as most puzzle games, they do get harder and introduce new challenges and the game slowly weens you away from the assistant of GLaDOS, the robot that operate the entire facility.
Some people might be wondering why I marked "Hard" in the difficulty rating? I'd like to amend this by stating that the central story of the game itself is somewhat easy, or at least just right for most users. It's the "Advanced" maps that got the better of me many time. They tax your ability to move from the beginning of a map to the end using the least amount of portals, least amount of steps taken, or by simply adding pitfalls of burning acid where there was once a floor in the old maps. Though somewhat difficult, there is an overwhelming feeling of satisfaction when you complete your goals and the achievement registers at the bottom of the screen, unless you looked it up on Youtube of course.
However, this would not be a proper review if I didn't mention that the majority of the reason this game received a 9 from me was the witty, refreshing dialogue that was offered by GLaDOS and the turrets. There was some comic relief to the robotic voice that coached you through several levels, and later attempted to tear apart your morale.
So, if you haven't played Portal yet and you feel that you even somewhat like witty puzzle games, then I would recommend preordering the second one, as I am certain it will be worth it, and you will receive the first one for free. Either that or log in or download Steam and purchase Portal for just $15.