As the title suggests, the game is fairly challenging, geometrically. The need to complete each level, combined with not being impossibly difficult makes the game addictive.
I only give it 4 stars because the animation of the folding takes way too long, and forces you to wait for it to be done before you can make another move. This can be agonizing if you’ve already solved the puzzle in your head. I hope to see the animation sped up, or given the ability to make more moves during the animation, in the future.