Excellent entry. I can see this being a very good browser or mobile game with some more polishing.
The play sections are short enough you will want to do one more run. The music is very satisfying as well as the sound effects. the visuals are simple, but in this kind of game, I think it helps a lot.
The only thing I believe may be needed is a medium difficulty as a step up, os some "pity system" on the hard version, and maybe some more layouts for the board (it is currently fine, but I wonder if some more complex shapes would change the difficulty). Really like it, good job!