It's entertaining for a couple of weeks. But you can't really have consistent success & move forward long term without purchases. The birds destructive power is grossly inconsistent between similar structures. For the effort put in, the rewards are dismal. You're lucky if you get arena tickets. When you do have a head to head match in the arena, you can have a higher level slingshot & 4 out of 5 birds ranked higher and still lose! You lose spells not used on a level, even if it's not offered!