An excellent game with quite a few laughs and some challenging later tests, but way too short
It's not an overly complex game to understand, and there are quite a few funny moments when listening to the computer as it talks to you. Graphically it's quite nice to look at, although sound effects and music are more run of the mill
One or two puzzles do require some pretty quick reactions and are thought provocing but otherwise they're not exactly Mensa quality, and I have already heard from other players that they felt the game ends way too soon, and that what they had played was a "tutorial" and indeed many of the earlier tests are tutorials
And this is where the game lets itself down. Tutorials are NOT levels and it's time developers relised you can't really count them as such. I was a good half way through the game before I started feeling challenged and tests were not taking less than 5 minutes to complete, and I wouldn't say I was especially clever!
To sum up, a brilliant game but lacking in longevity due to the lack of tests. I would say Valve's intentions are to release more tests in expansion packs, most likely via Steam. I've given the game 8.5 because overall it is a great game, but it's not getting 9+ due to the shortness of the game.