LittleBigPlanet. But the levels were barren and flat, and devoid of obstacles, so the player moved upon the face of the level creation system. And the player said, "Let there be swinging, spongy balls," and there were swinging, spongy balls. And the player saw the swinging, spongy balls, that they were good, and he divided the swinging, spongy balls from the electrified floor.
If you needed any more proof that LittleBigPlanet's level creation system is going to be mind-blowingly robust, (though arguably less robust then the level creation system discussed in Genesis), we turn your attention to the video posted after the break -- a time-lapse sneak preview of a player crafting his own level. It's a pretty clever design, and looks like a blast -- best of all, it only took about ten minutes. That kind of thing apparently used to take seven days. Thanks, technology!