Amazing work, your game was very fun to play through, though I barely used the upgrades at all, since the cost of towers was the same of the first tier of upgrades, and it would not increase no matter how many towers I had, I just spammed those towers, and won very easily. Also after wave 3 I think, the health bar of the enemies was empty, but they would still take 2-3 hits before dying, so I found that really weird. The graphics were amazing, hope you add more stages, towers and enemy types later!