Well,
This is a very good game.
I enjoyed playing it. I never paid, and struggled through hard parts. To me (merely an opinion, not a criticism) it got old halfway through hard... so I stopped then. It was very fun otherwise.
I liked the animation. I liked the audio. I liked the way you got the upgrades after the acts.
There is one thing I didn't like.
Your introduction through your Author Comments seems very defensive about your method of gaining money through the game. I have to say that this is a simple "spin" on micro-transactions. C'mon guys. Don't try to fool anyone. Call a spade a spade. If you're going to have a micro-transaction system, don't try to deter or misdefine or etc. I'd play this game all day long, and at times, I truly wish I had a few more diamonds... but my thoughts always went back to the obvious micro-transaction you introduced me to.
I suggest developer (marketing?) transparency in the future. I hope you don't take my response negatively. I think you have a wonderfully good product that kept me playing for a while.