As in most things of any importance, there's no right answer to this one. It's safe to assume that customers who buy 1000 piece puzzles want a challenge, otherwise they'd buy a poster. That said, people have different amounts of tolerance for difficult puzzles. To the degree possible we strive to publish puzzles where every single piece has clues to what part of the puzzle it belongs, not just the border pieces their flat sides. We think bright colors and random, hand drawn shapes add to the fun. We like challenges...figuring out what part of the giraffe a piece fits on our African Animals puzzle goes can be hard. Figuring out the difference between the backgrounds of the car puzzles, and finding streets and cities on our map puzzles can be challenging, but worth it......way better than finding a blue piece in a huge patternless sky.