I played the extensive demo. It's really, really good.
Since you brought us Minecraft, I now have to believe everything you say.
…yeah, this game is amazing in a simple way. Nothing to deep, but somehow..... it is.
Did you ever play
Elite 2: Frontier? Famous old space game. Minecraft reminds me of this game—completely open-ended. You do whatever you feel like doing.
I think the aspect that seals the deal is the danger. If there weren't monsters out there; if you didn't have to seal yourself in a home or a tower or whatever you can imagine; if you didn't have to be careful about how you mine, I don't think it would be quite as interesting. Its simplicity is its beauty. It gives you tools, creates a world, and sets you free.
The more I discover, the happier I become with the game. I'm enjoying finding pumpkin fields and cascading waterfalls. I've caught a few glimpses of lava but it's not near my home.