To me, the more interesting part about minecraft's success is that it gets a lot of people doing things that look like work to me for fun. Also, it does this with a high learning curve and without using any kind of reward schedule mechanics that are in vogue now. As far as I can tell (and I've only watched others play), the appeal is based on the joy of creation and sharing your creations, and the difficulty of it actually enhances the experience. It just seems so fresh compared to what everyone else is doing.