Very fun short game experience! It's a simple and easy to understand game loop so it was really easy to get started right away. Art and visuals are also great! I really like the overall vibe/aesthetic, not only in terms of the visuals, but the music and sound as well.

Overall I wish the gameplay was a bit faster paced (shorter length for the waves, more opportunities to buy upgrades, etc.) as it felt a bit slow or repetitive after a while. I think especially just offering more upgrades / offering them more often would help keep things interesting for a bit longer.

Also I have some nitpicks about the UI; for example the color of the text doesn't have enough contrast in front of the dark background.

Great job everyone! Have fun with your free courses! :D