I actually never played Portal all the way through, and as such I am not as big a fan as others here may be, but that does not take away the awesomeness of the app. For me, what really did it is the accuracy of the targeting. I found myself running around my room trying to figure out where I could and couldn't hide. Also, the laser targeting is a really nice touch (and yes, I know they were already in the game, but I am referring to its accuracy and the fact that it shows that it actually knows where you are, and not just that it detects some random movement.) I may not be a programmer, but I can tell that took a lot of prior knowledge and skill. It makes me wonder what other technology can be adapted from video games.