The concept is pretty fun, even with a lack of plot. However, income even from 3-stars victories is too low (+100 is not even enough for 1 upgrade). Upgraded units increase in price makes it impossible to play if you haven't made enough hero upgrades. This two things combined quickly turn playing into grinding previous levels for money which is not fun. The graphics and music are nice though, so it needs some economics/difficulty tweak to be really ok.