I'm not sure I get it.  Other than watching some hilarious videos on YouTube, is there anything else that draws people into this?

I'm not sure I get it.  Other than watching some hilarious videos on YouTube, is there anything else that draws people into this?

I think the simple mechanics and freedom to build are the biggest draws.  Creating almost anything you could want may be daunting for some, but an amazingly freeing and engaging experience for others.  There's also a bit of collection and hunting for rare ores.  Finding your first diamond vein is exciting, until you realize that you don't want to use any of it till you find a lot more, so the quest continues. 
 
As it is right now it's not a game for everybody.  It's still got a long way to go, but the potential for something awesome is there.

Being part of a game thats still in development by an extremely personable creator who adds new things to it every week (usually).
Other than that you have to be in a creative mood to actually do anything worthwhile in it now. I personally like building traps to harvest meat and leather.

I haven't played it, but from what I've been able to watch (and that's been a lot) when you actually get to play with a virtually unlimited Lego set that you can live inside, and use to keep out the bad, grow things, and discover new places, it's sort of meditative.  It's one of the few games that actually takes that user content thing and really runs with it.  You still, in survival mode at least, have conflict in the form of things that spawn in the dark, and there are treasure chests to find guarded by Gauntlet-like monster generators.
 
Also, because it's a virtual world, the consequences are minimal, so you can have fun risking your avatar's life doing stupid stuff, like stuffing a mountain full of TNT.
 
Another thing is that new features come out pretty frequently. It's one guy adding things to what is a pretty modular system, so it doesn't take much for a completely new, game-changing element to appear. Means there are always new surprises on the horizon, at least for the foreseeable future. 
You also sort of figure out the rules of the world as you go, which to me at least is always a draw.  When things are nice and consistent like that, it's neat to be able to build off those rules and make interesting contraptions that couldn't exist no matter how many Lego sets you had.

Think of it as a giant kids' sandbox that you can build anything with - the draw is in the open-ended creativity. If you want to make the world's largest castle, you can go for it.  If you want to build a rollercoaster - cool!
 
I think its biggest virtue is that you don't have to be weighed down by a direct line adventure. The adventure is in the exploration and the building.  The music and lighting should also be mentioned - both are done very well.