Fun tower defender game! The music backing track was really lovely to listen to. I liked when the units started getting more challenging like the orange guys that moved faster and took more hits to take out. As some reviewers already mentioned, it would be nice for the intensity of wave 21 to start earlier but I see how mentioned adding a wave timer adjustment in a later version. Also, with the screen ratio it looks like this could be a mobile game eventually? I think it would be really fun to play on mobile if you add upgrades.
Great work!