Yeah, I'm aware of the balancing issues, and that's the primary goal of the next release, besides some juice here and there.
I haven't had anyone tell me the shooting sounds like farting, but that made me laugh way too hard. I thought the "Ding" would be funny, but I take it you didn't find the easter egg associated with it. As for alerting the player how to buy ammo, the next release will contain icons at the bottom-right showing the key to press to open those windows. I only hope the icons are obvious enough. I also have text now when you level up saying "Press T to Level Up!".
As for your notes...
1. Everything is a balancing game at the moment. But the feedback definitely helps. It's hard figuring out which weapons should be unlockable first. I figured having an automatic would be nice early on, so I think I'll make the Assault Rifle more expensive and add an SMG or something. I'm also planning to add level restrictions to certain weapons.
2. All the artwork is either from the original game or placeholder artwork until I get around to remaking everything. Girlfriend is working on the concept art so I have an actual art direction to work with this time around.
3. Unfortunately the music isn't there to stay since it's not mine and is just a placeholder. Eventually, I plan to write a genetic algorithm to sample the songs I like that follow the art direction and evolve new, original music.
4. They use to moan, but I couldn't stop laughing at how ridiculous it sounded because I recorded all their noises from my mouth.
5. Yes, it's intentional, but I'm thinking of making it brighter by default. You can adjust the darkness in the Settings -> Display menu.
6. Audio levels can be adjusted in Settings -> Audio. I need to add a way to access these settings from gameplay though.
9. The size of the flashlight has changed like 5 fucking times. It's likely going to change another 5 times before the game is done.
10. That I haven't heard before, but I'll look into making them more obvious. My particle system is very basic at the moment, so there's only so much I can do to make them interesting. Do you think making them thicker would help? Or is the long rectangle shape what's wrong with it?
11. Yeah, this and being able to access the shop and training screen at any time are being considered. I'm thinking of changing it so those menus and pause can only be used between waves, but I'll have to make ammo more common so the player doesn't run out. That or add melee weapons, which is planned.
13. Are the grunting noises not loud enough? I'm trying to think of a visual effect that could work.
14. There is no difficulty progression at the moment. I need to think of a good way to scale enemy stats and make it harder. I do have more enemies planned for future releases though.
15. I figured 3 was pretty standard, but maybe health should be lowered.
16. Is it mostly the AK-47? Or all of them? Because I'm aware that the AK-47's sound is obnoxious.
17. That will be changed.
18. What do you mean by this? That they can still damage you while YOU'RE off-screen, or while they're off-screen?
19. All the powerups have arbitrary drop rates. I'm just using user feedback to adjust accordingly.
22. I'm hoping the level restrictions and increased price will mitigate that somewhat. Not sure how else I could fix it.
23. That's expected with the amount of content it currently has.
Thanks for the feedback! Hopefully the next release will be less boring.