The game is based on gems. There are plenty of opportunities to collect them. What made me rate a one is the customer service. I had accumulated over 80000 diamonds and one day half of them disappeared. I contacted customer service and they wanted me to use the reporting function in the app itself. The date they disappeared and all that. While I was filling out the form the game closed on me and when I restarted the report function was gone. Then they banned my account for no reason.