Let's let the man explain: "Basically players can control and stretch Boy, the main character of the game. As players stretch Boy, the lengths to which he grows are uploaded to a persistent character known as Girl, who grows at the same rate as the combined length of all the players in the world. Girl starts at Earth and expands around the solar system. When Girl reaches a new milestone in the solar system, new areas are unlocked as playable stages for everyone around the world."
Cool. But why did Takahashi make a game that's seemingly so hard to define? "By making an undefined and ambitious game," he writes "I want the player's reaction to be something like, 'I don't know why, but it's somehow interesting. I can't stop playing.'"
You know, you could've just given us a video of Boy humping a rainbow while ostriches milled about his flaccid body, Takahashi. That's pretty self explanatory.
Noby Noby Boy Is... [PlayStation.blog]