This is a pretty good game. Sometimes the puzzles dont register that they are done and correct, and then if you leave the puzzle it resets. A "check" or finish button might help this. Also, I love the background color, but when there is a row/columns with a lot of numbers, the outermost are very hard to see when they are blackened, which makes knowing where you are in solving the row rather difficult. Maybe just leave more space around puzzle before darkening background.