Pretty sweet!
I've never seen this type of puzzle before, a three-dimensional sliding block puzzle. I like two-dimensional ones, so I had fun with this. The program was very well done. I especially like how you generated the puzzle by sliding, so as not to get any impossible situations! There were only two minor issues I had: 1) It was hard sometimes to see the "in-between" colors to make sure you knew which piece went where. 2) The arrows seemed like they didn't always spin the cube the way I wnated. And you technically need another pair of arrows, for a third degree of freedom. But that was just a minor inconvenience more than anythign else. All in all, great job!