Reduce AP cost and make them WAY easier and cheaper to get. Gameplay has used up all AP in an hour or less. GOLD stars...2 in a bundle? Get real, I need like 400 for an upgrade...what?
Otherwise, fun game, just after spending a lot of cash, it is frustrating to run out of AP, especially at your price to re-up them. Like playing an arcade game and having to put 2 extra coins in than you previously put in...just to keep playing. I pay for the upgrades, not the right to keep playing.