This is a really cool game. Pretty simple but somehow very addictive :). I love your interpretation of the balancing mechanic. I was missing sounds and music, which would make the game much more engaging. Additionally the stats are very small on the units and there are a lot of numbers on the screen. Maybe adding health bars instead would be more pleasing to the eye :).
Congratulations to this very cool entry! I really enjoyed playing this. Keep working on it!