I finished Portal tonight because I had to finish it. I started yesterday and got to the final level but didn't quite have time to finish, so naturally... It is an amazing game and I'll be thinking about it for some time. Aside from the ingenious game mechanics and level design, the sheer amount of personality that was imbued into what is essentially a game with only 3 (maybe four if you include the Weighted Companion Cube) characters, only one of which (yourself) is alive, is amazing. Once you finish the game you are treated to the following end credit sequence, which I recommend watching only if you are sure you'll never actually play the game, as the pay off after finishing it yourself will double the pleasure of its viewing.