This isn't anything too unique, as there are hundreds of sudoku flashes out there in the tubes, but the presentation is very clean, and I like the ability to hide and show possibles. 7/10.
Side criticism: I've never been a fan of the patronizing "ta-da" winning sound file.
There are a couple of methods people use to complete sudoku on paper, I suggest you discover them all and allow the player to choose which aids they want. This would provide a complete sudoku experience.
Yeah, but they are already in the game.
For example, you can see the option of putting "Possibles", in the small blue rectangles.
I mean: you can already implement the usual methods for solving Sudokus.