The difficulty level variation is a bug downer on a game that is otherwise very playable and nicely put together.
Some observations about the difficulty:
1. the "normal" setting feels like the "hard" setting on comparable games; adjusting to "easy" is not an option because that actually is very easy
2. The levels aren't consistent in difficulty from one level to the next.
Good luck with improving the game!
 "Minions"){kind=icon}
 "Frontline Defense First Assault"){kind=icon}