The damn ads! I was enjoying the game, but only 4 levels in I was getting an ad after every level! Because the levels are short it was an ad every 20 or 30 seconds, and each ad was at least 10 seconds. It became unplayable. I considered if I should pay for ad free because I was enjoying the puzzles, but the "no ads" button was just for display! Obviously they make more money from the 10 ads they would from charging 99c for an ad free experience.