This is simple and clean. Why dont you add score and no of moves/rotation player did?
But I feel this do needs some kind of gamification and proper ordering of levels. As twice I received simple puzzle after completing some harder!
Plus if possible do change some colors once the loop is completed. I felt those colors are like olden days. Rest whole game has cool colors.
There were quite a few suggestions for level number, so you could feel your progress, so that might be the only visible feature in version 2.