Upgrades too powerful!
Oh no! This game is pure gold up to level 10, then upgrades start getting too powerful for the enemies. Once you get 20 archers or so, you can just sit back upgrade when you can, reload archers and click the occasional catapult. I'm actually playing level 17 while writing this review.
Aside from this, the game is really awesome! In the next version, please make the cost of each susequent archer double the last one or something, and cap it to 10 archers.
As for reinforcements, I'd say 10hp per upgrade would be good, and again, double the cost for each reinforcement ($300, $600, $1200, etc.).
(Also a music switch in the game would be coolasd)
This game is awesome. I beg of you, make these changes for the good of Newgrounds!