Awesome game!
That's a great game you made. Here's my opinion about it:
The good:
1. The song you chose for it fit perfectly. I loved listening to that song while playing.
2. Graphics where great. I didn't expect the graphics to be so good.
3. Gameplay was also good. I play this game almost everyday.
4. Special powers where awesome alto the bomber could do more damage since it's preety hard for the bombs to hit enemy units.
5. Nice selection of units alto it would have been good if you added a "Dragon Rider" instead of a Knight in the second era.
The bad:
1. One of the things I didn't like was the high power and range of the Ion cannon turret because when the enemy soldiers where killed, the remaining bullets hit the enemy base. Which was a real easy win.
2. The background always stayed the same. It would have been better if after each player upgraded to the next era, the background would change. Example: First era with trees, second with trees and a distant castle, third with a village, etc.
3. I didn't like the special of the third era. You should have added, lets say, one of those jets that where first invented that only had a rapid fire-chain gun that could sweep the battle field and do multiple small amount of damage to enemy units.
Well thats all. Really nice game. Great job!