This would be a very nice mobile game. I do agree with the others that an undo button would really improve it, also a reset button to revert all pieces to the original state would be nice too. The difficulty is all over the place though. Some levels are incredibly easy while others are much harder, with some playtesting I'm sure you could rearrange them into a friendlier difficulty curver though. I like it.
I also spent way more time with it than I was expecting.