'Fallout Shelter' Is Apple's #1 App, but Embodies the Shallowness of Mobile

As South Park said, this is the problem with all freemium games. You need to make the game somewhat fun (so people will pay), but not too much fun (so people don't feel obligated to pay more so it's more fun).

When you design a freemium game, your target audience isn't the guy who plays it for free or pays $10. Your target audience is the person who gets addicted and spends $1000+, due to the power law nature of spending.