I really liked the music! The main song is real banger! I wish I could make music like that! Thank you for noting that you took the song from pixabay.com - such an interesting resource I didn't know before. I hope I can incorporate some music from there in my own games in the future! I also liked the game's sound design.
The art is clean and concise, with good readabilty.
I liked the idea of leveling up. The moon functions like the bible in Vampire Survivor, which I like. I wished I could make the moon more overpowered, though. It felt like I didn't get much use out of it in the beginning of the game. And I wished I could make it more powerful a lot quicker, but maybe that would destroy the game's balance.
It is a clicker game, which I imagine can be exhilarating and is a core part of this game's getting-better-by-aiming-better-and-clicking-faster mechanism.
But I wished it was not one shot per one mouse click on the incoming "germs", but rather, a barrage or stream of bullets through holding down one key or mouse button. I am not good with clicker games and clicking so often in such a high frequency made me feel slow, inadequate and a bit frustrated with my slowness and slight feeling of exhaustion in my clicking finger.
My preference would be: Aim with mouse, hold down a button to fire a stream of bullets. That way, you can level the shooting as well, e.g. more bullets in a shorter timeframe, faster bullets, spreading bullets, stronger bullets, homing bullets, maybe left click = many weaker bullets, right click = single mighty bullet with AOE and cool down. This would be my personal preference.
Also, I would like more "helpers" in addition to the moon. Maybe spawn space ships which fly around the planet and shoot down germs on their own. The space ships could also be leveled up. I want to have the feeling of: "Hah, you fools! Come at me all you want! My mighty space army will shoot you down in an instance! You shall not pass! You don't stand a chance!", or something along those lines.
Managing and balancing
a) feeling powerful,
b) aquiring more power and feeling satisfied to do so,
c) the feeling of being challenged and therefore
d) making the feeling of success and victory possible
is difficult, but I think if games can strike this balance, they will be very fun to play.
Also, give the option to evolve the moon into some kind of Death Star, which shoots germs down on its own within a certain radius.
Given that I started imagining the game's progression while playing it, shows that this game provides a solid base to be build upon and expanded. Good job, developer :)
I hope it was okay for me to list my ideas for the game. Personally, I learned a great deal by reading the comments of people who have played my game - which suprised me alot! -, so I wanted to pass on this favor. I hope I do not come across as someone mean, who just lists of odd things just to construct a criticism. Playing the game, I had the impression that it was made by an experienced game developer, so rather than only listing superficial words of encouragement I wanted to list things I wished were in the game, to inspire for improvement and expansion.