Wow! My 14-year-old mouse burned a hole in my desk. Very cleverly constructed game design. You managed to make a very addictive game. And I think you even completed the Make a game with only particle effects challenge.
The visuals are great. The level texts are funny. The upgrade system also worked well. I really like how the music dynamically adapts to the difficulty level. At first, it bothered me that the background music always started from the beginning and I couldn't listen to it all the way through. Because the cycles are only a few seconds long at the beginning of the game. But then I understood that this is part of the concept.
By the end, the game plays by itself. I also maxed out the upgrade tree.
Great game!