This is a great game. Excellent programming and good interface. Its intuitive enough but maybe you could clean up the screen UI a bit. There's a lot of junk on screen that can confuse or distract a new player and some of it isn't all necessary or vital to know.
I wish the battles moved a little faster, but I was impressed with the upgrade features and the styles of units. I also liked how easy it was to move around my units and you added features to help easily assign formations.
I think for a flash game, you balanced the number of unit classes well, not having too few or too many. I also appreciated the game hints. They actually had useful information from time to time.
For future versions of the game, I would love to see the option of building (such as walls or towers.) Like I said before, I think the game would be more addicting if it moved faster.