I enjoy this game but the challenges are not fair. I continually pass all the levels and buy all the upgrades I am supposed to and when I excel at the challenges the game will always make the next challenge a number of coins that is too high for what I am capable of doing within the limits the game sets for me. I have to go back and play other hotels I have already beaten to try get the next amount of gems needed for the next upgrade. I think the game tries to make you buy stuff to move ahead.