The developers created a great game that is fun and challenging. Ads are not shoved down your throat, availability of rewards is fair, and upgrades aren't too expensive. Paid upgrades are not required to play the game, but it makes it easier to play and more fun. I found a game I don't mind spending money to play. Update: I agree with another player the card tent is rigged. I played the same card for over a month and never won the measely 7000 energy. I quit opening the tent.