Thanks for the feedbacks from you guys I made an update for the game which makes playing the game more enjoyable! To make filling the gaps easier now you can use the numbers on the keyboard as hotkeys. This function is available from the 9x9 sudoku puzzles (level 5).
Another big update is that now you don't need to replay the game if you want to reread the stories. You can read every story part if you solved it before of course.
Good luck for everyone for the puzzles!
Cheers,
Balazs