Okay game with a fairly simple concept, however it quickly degrades its own balance with the upgrade system that is put into place. Units that are not upgraded become worthless as even the unit they hard counter can destroy them, and for all the damage I think I'm doing to enemy units with towers or arrow barrages, It's impossible to tell what is doing anything as the levels progress.
The one thing I did come to find is that wizards are vastly overpowered, as their range and speed makes them simply better catapults, and the only unit that seems to "counter" them is the worst unit in the game; the sword. Even then the sword units were continuously getting beaten by enemy wizards to the point where I could do nothing if the enemy just decided to swarm wizards on me.
This premise could work, but it's a game that depends on a strong balance and rock-paper-scissors mechanic. It should be focused on that aspect first, and should severely downplay the boost given with the upgrades for all units.(With that being said, I honestly don't think any of the numbers listed for damage and life are accurate on the upgrade screen, as after only 1 upgrade wizards have 300 health while the horse upgraded twice has only 45? Doesn't seem right.)
Finally, the game could really just use a bit better elaboration on the various elements of the gameplay. What do the different towers do? What is the "Guard" upgrade for? Maybe a simple health bar over units so we can see damage tracked and make better decisions.