While I know this doesn’t comprise all of the content found in games like LittleBig Planet, but it composes enough of it. One reason I never got hooked onto LittleBig Planet is because when I tried it out and played the top rated level, it was boring. It was slow, felt a big sluggish, and the level design had me just stumbling around to solve answers to easy puzzles.
Also, whenever someone wants to show off their amazing stuff, it’s always derivative material. My friends thought they could get me into the game by showing off a Metroid level, in which my response was that I could just play Metroid to get a better experience. I think that user-generated content is great, and certainly platforms like the workshop for Skyrim and Portal 2 have shown that great things can be made. I don’t think it’s an inherent problem for games to based around user-created content, but just a prevalent one where the most common things you’re going to find is people trying to mimic something else.