Well, by accident, I managed to finish Portal in a single day. Sure, I would have liked to go through it slowly and have a look at all the scenery, but when you get immersed in a puzzle like that, you become like a lab rat in a maze: the cheese doesn’t even matter anymore; all that matters is the goal.
Still, despite that, Portal turned out to be one of the best games I’ve ever played. It’s definitely the best first-person-shooter-like game I’ve ever played. The environments were perfectly designed, the puzzles were challenging, but not brain-hurting, and it was incredibly, incredibly immersive. It was so immersive, in fact, that when I became trapped in a room filling with poisonous gas, I realized that my heart was actually hammering. (People who have played Portal will agree with me…for everybody else, that’s just a cruel teaser).
So, my previous conclusion stands: you should buy Portal. If you can’t buy it, or don’t want to, find someone who has (and no, you cannot come to my house. Don’t even try it. I keep vicious attack ostriches).
And one last note on Portal (this may be a semi-spoiler, so don’t read it if you want to keep all the mystery intact):