Well I absolutely love it.  As far as sandbox games go, it's about as sandbox as you can get, which is great.  I've been programming in Java for about 2 years now and I want to foray into gaming development but I've never dont anything more complicated than a frogger type game.  What are you using to generate 3d graphics like that?  Is your cube system basically a 3d array where each cube space can have a different state, each one being associated with a different texture or not one at all?  This style just fascinates me so much.  Excellent game.