Unfortunately, it seems to be one of the most over-hyped games of recent times.
It's amazingly polished, extremely cute, and has an astonishingly sophisticated level editor.
Sadly, the game itself doesn't seem to be very playable. At heart it is a fairly basic 2d platformer (though one with a nice physics engine). This is no bad thing in itself, but the developers seem to have missed the point of a 2d platformer. The controls are imprecise and frustrating. The story levels are also frustrating - I've no idea what they were thinking with having a small number of lives and making the player start from the beginning each time. This was acceptable in the 80s but everyone else has moved on in game design since then.
It's possible that I've rather missed the point myself. I'm sure it's possible to have a lot of fun messing around with it in multi-player and coming up with new levels. Unfortunately, to unlock most of the objects for the editor requires you to play though the story levels, and I suspect that I can't be bothered.
I just hope that another developer will be inspired by the ease-of-use of the LittleBigPlanet level editor to do something similar in a game that is actually worth playing.