Well, that was my first question. I don't own a PS3, and so hadn't played LBP before, but was of course aware of the hype. So I bought it to find out.
LBP is a platform-style game, where you take "sackboy" and have to overcome a series of challenges and obstacles (mazes, lakes of fire to swing across, electric plates that kill you on contact, etc), to reach the end and finish the level. Along the way, you collect bubbles which accrues you points, and also contain goodies (like new items of clothing to change the appearance of sackboy, and stickers, to change the appearance of everything else. The levels are regionalised, so you start in Australia to complete several "Australian style" challenges, before progressing through South Asia, India, Africa, etc. It has a superb sound track, great in game sound effects, fantastic graphics, and of course the expert narration from Stephen Fry.
Is that it?
No, not by a long shot. The included levels are great fun and would form a good game by themselves, but after that, you can play levels created by others by going online. And if that still isn't enough, you can even design your own, using all the stickers and objects that you picked up along the way (and I assume with future DLC?).
So it is vast, vast, vast product and will keep you going for a long time.
If you played it on a PS3 and liked it, I am sure you will like this (portable) version. If you haven't, you owe it to yourself to give it a go!