Nice work
I enjoyed this game, even if it was a bit repetitive.
I beat it in normal mode as follows: go to last age, build 4 best defensive turrets, then wait till you have 550k (from your turrets shooting the incoming enemies, they can't harm you because your turrets are too strong), then sell all your own turrets to have some 200k more money, and build 5 of the best unit. Then your 5 units simply own the enemy (combine with the special to make them win faster) and victory!
That was normal mode though, I must still try the harder modes.
I'm not sure if it's a bug of my flashplugin (which sometimes doesn't display text) or something missing in the game itself, but I had no info about anything like the price of buying a unit. If that's not due to my flashplugin bug, then, it could be a good addition to the game to have some info about the units you can buy show up if you hover above it with the mouse.