Because there is absolutely no difference between the game Sudoku and our game Toon-Doku, except the look of the individual pieces, you would expect to see very clear delineation between pieces. My problem was that there were too many similar pieces right from the beginning. With the screen size, I found myself squinting at many of the pieces. I thought it was only me, so I did a little play-testing. A lot of younger kids had the same trouble. You can zoom into a square, or grid, but in a game that requires you to view all of the board all of the time, this made it hard for younger kids to switch back and forth. This is quickly fixed as you gain new pieces and can really vary the look, but right at first with no adjustment, it can be hard.
As expected with any puzzle game, there is a looping soundtrack in your future. Luckily there are five to choose from. This may or may not be a good thing depending on the number of hours you will spend playing it.