Wow, 4 mediocre reviews from here. Why the hell is this thing getting such godlike reviews from EVERYONE!?!
Because of people like me who think it's great
The levels included in the game are really fun and some are very challenging (especially if you're trying to "ace" it to get the extra items). My kids love it (wake up everyday saying "can we play little big planet?") and I'm fairly addicted too.
I guess how much you like the game really depends on how creative you are, because the "create" aspect of the game sets it apart from just another platformer. I completely disagree with the person saying the create mode is un-intuitive...it can't get much more intuitive with the flexibility they give you. Rods, bolts, explosives, switch triggers, emitters, wood, sponge, metal, etc... You can really create anything you want. Just walk through all the tutorials and you'll pretty much have it, IMO. If you want good levels, obviously that takes commitment...but as far as "intuitive", it's all right there with your right thumb

The flexibility in the create and the physics involved is really just amazing. As mentioned, there is some garbage on the created levels, but there are also some gems. I find 1 or 2 every time I get online that are like "wow, that's very imaginative!" To see the possibilities, just search around youtube for a bit
http://www.youtube.com/results?search_query=Little+big+planet+best+online+levelsMy main beef on the game is the search, as you "heart" levels, but there's no way to search for the most hearted levels (you can see which has the most as you browse, but can't filter by that to narrow out the garbage). They really need to fix that.