It's exactly what I look for in a good puzzle game: easy to understand, difficult to solve.
Some small improvments could be made, however.
- the playing tokens (or whatever you call the thing with the numbers on it) look bland. It would go a long way to make them pop since they're on the app's icon.
- it would be more intuitive to be able to drag and drop the tokens along the board instead of swaping.
- there is no way to exit to the main menu.
- I don't know exactly how many puzzles there are but I ran into the same puzzle multiple times once. The more the better. If it were me, I would write a program to help make new puzzles faster. I hope you're not making each by hand.
- have the token light up when the right amount of tokens are around it. That would help people understand it faster.
That's all for now. I highly reccomend this game and I hope you plan to update it.