If you'd asked me a couple of weeks after I'd bought LBP- I'd have said it's brilliant. One of the best games I've ever played. Now, months later, after the dust has settled- unfortunately, I don't think it's great. Good, but not great.
First the good stuff. It's beautiful with a great atmosphere to the game. Stephen Fry narrating is genius. The story mode is good fun (though short) especially if you play with someone. The level creator puts level design within the grasp of anyone. If you can imagine it, you can make it. Plus, you'll never run out of levels to play. Some of the user made content is amazing (some of it rubbish). And, it's a basic platformer at heart.
Now the bad. The controls are sluggish- not so bad that you can't play but bad enough that you will occasionally try and snap your PS3 controller in half. The level creator is temperamental at best. You'll be half way through making something and it'll break- for no reason. Also, making a level is a huge investment of your time. Plus, it's a basic platformer at heart. The lag when trying to play co-op online made it almost unplayable- though this may depend on your connection. And the worst; the way level designers are treated is poor. The chances are you'll spend many hours making a level and it'll get a few plays. Unfortunately, your level is a drop in the ocean. Your level will disappear into obscurity and after a week no one will be playing. Think your level is different? It's probably not. A simple -Play a random level- option would have got round this. But no, despite the improvements in the search level function, your level will probably disappear without trace.
You could be unlucky and your level gets banned/moderated. If your level is moderated it's all over. Your level, that you spent hours/days on, can be moderated without warning or reprieve. Media Molecule have been continuously criticised for their moderation and I have seen no evidence of the improvements they claim to have made to the process. If you're moderated then your level is likely to be gone forever. I'm not talking offensive material here; their moderation is, for the most part, there to protect themselves, particularly with regards to potential copyright infringement. It's totally against the atmosphere, and style of the game. For a game that is made around user-made content, it's a shame they treat level designers so badly.
I've included "it's a basic platformer" as a good and bad thing because it depends on what you like. I love platformers (I've been playing them for over 25 years) but if you don't like platform games, don't expect this game to convert you.
Basically, this is a good game that you should buy. For 17.99, it's a bargain. There is plenty to enjoy here and I certainly got my money's worth. Is it the gaming revolution that everyone was hoping for, or something you'll be playing in three months time? No, probably not. Are you a level designer (or potential level designer)? Good luck. You'll need it.