Too long, and too strong.
The units you give the player are simply too powerful. I expected that they would die, and I would have to replace my lines mid level. This wasn't the case at all, in fact, a few archers and you win. One thing I would have liked to see was a health bar, on both friendly, and unfriendly units.
The levels were painfully long. In fact, the only thing that stopped me from leaving my invincible archer army alone for twenty minutes while they fought a depressingly one-sided battle was the awful method of collecting money in the game.
In short, make the levels at least half (I would prefer a third) as long, weaken the units, and throw in health bars.
p.s. The type font you used was difficult to read, pick something else. I don't care if a word looks pretty if I can't read it.