This is a fun game. Enough of a challenge to keep me interested but no rage quit moments. I do admit however that level 29 was tough to finally get right. Nice job devs. 5/5.
I like the game, fun to play and make progress but not so difficult as to cause rage-quit. One odd point though is that on the front end you are frantic for money and later you have enough to buy the world but are scrambling for experience. That might need a little balancing.
I note that there are 3 badges, one easy and two medium. How about a hard (maybe impossible) badge for killing 100% of the enemies on every level? Just a thought.