I would give it four stars, its a really focused and detail oriented game. But, the game shows ads immediately at the end of the game, whether you've won or lost. I understand keeping the game free to play with ads by option for upgrades and other freebies, but forcing your users to watch ads every time they play a level is not acceptable. It's predatory level of marketing. Also, almost all of the higher weapons and upgrades are locked behind a paywall, and only accessible by paying.