Portal is a game that involves using the namesake portal gun to pass tests set up for you. I have heard (haven't played it yet. need to!) that it is a great game. It has a creative storyline and sets itself up for sequels perfectly.
Fans have picked up on that and many parodies and fan pics have come of it. Even without game knowledge these are just plain interesting and paint a bigger picture of what the game is like. Many fan creations that I know of have beome popular on the internet, and that may be attributed to the pure popularity of the game. Even several sayings such as "The Cake is a Lie" and "Im in SPAAAAAAACE!" have beome popular.
