I played the first 100 levels and the puzzles never got harder (and they're already much easier than you'd expect). You also earn coins and puzzle pieces, but it's never clear what you're supposed to doing with them. That energy should have gone into making better puzzles. As others noted, it's packed with ads - there's one after almost every level, and the ads take longer than the level. If I have to watch an ad to open the "gift" I won, then it's not a gift. Disappointing.