This game is challenging but not so impossible you will tear out your hair in frustration. Because there are three 'hidden' stars, effectively there are four levels of difficulty for each puzzle, and there are 110 puzzles (currently - I hope there will be more soon!) so there is a lot of fun play time. When the puzzle is solved, the screen lights up beautifully; it is very soothing and gratifying! It is a perfect mix of challenge and reward in a lovely format! Excellent game!