Hey, I like your game! And I appreciate your organized approach to this thread btw :)
My favorite part of this is probably the satisfaction of playing it in general. I get that it's supposed to be exhilarating, but to me it's actually kind of relaxing... Just something to mindlessly do when you're bored. The mechanics and graphics run very smoothly, I actually am curious about how to get things to be so fluid and pleasing to the eye. The upgrades are cool and efficient, music is fire, everything works well.
The only thing I would say to improve is maybe the engagement with the player. It's a fun game, but I think it can get a bit boring at times even with the upgrades. Maybe add a bit of a story (I can help with that if you'd like), or maybe a difficulty progression that feels even more rewarding than the upgrades? Idk just throwing stuff out there
Feel free to check my game out, I could use your feedback: https://wasabiiii.itch.io/grass-elemental-demo-demo
Something about this is just really nice to look at, with the smoothness of the movement and sprite animations. I hope to one day be able to achieve that with my work!