This is a clever little puzzle game, and it is nicely executed.
There's a room for improvement though. As previously stated, adding an in-game tutorial would help. Also, don't forget about music and sounds - these go a long way to make the experience more enjoyable. To add more game juice, you may play around with some animations here and there as these would make the game feel even more satisfying to play.
Good job on puzzles and mechanics!