Portal is the best computer game I have played in ages. You play a research test subject who uses a portal gun to navigate through a bunch of different levels, with the reward of delicious cake (and grief counseling) at the end. It’s fun and challenging, and it’s got this lovely streak of dark humor running through the whole game.
And at the end, there’s a great song by the incomparable Jonathan Coulton.
My only complaint is that I wish there was more of it. The main storyline will last 2-4 hours at most. But considering that it is only a $20 standalone title, its entertainment-time-to-cost ratio is about the same as a really good movie.
You should definitely see the trailer for the game if you haven’t already.