Well consider this game took $0 to make (not counting the greenlight fee) and I had to design all the art by myself, I wasn't able to get someone to try help me polish the graphics until late in the development, but even then there was no way we could have fixed the issue of repeating backgrounds you are talking about. I wasn't freeloading or through this, my life conditions simply were that crap at the time when I was starting out.

Not having a dedicated background artist does this, this might not be a problem in future titles depending on budget and overall cooperation. I'm not saying you are wrong, you are correct it's an issue but it's something that was unavoidable, I COULD have attempted to draw so called "Long backgrounds" but chances are the results would be even worse.

or just plain black background

One thing i dont like is after the mini boss of stage 2 the bullets are nearly invisible on the background the lack of definition doesnt bother me just that small fact. Maybe chaging the bullet colour for that enemy type would fix the problem.

Well, I had that debacle with that bullet type before in terms of color clashing in the development many times, and nobody agreed on anything in that department from the testers, for whenever I tried to fix it there was someone who wasn't happy with it and the cycle kept going :P

You should think of adding a color-blind option.
Some projectiles were pretty hard for me to see.

Came here to see if anyone else was having this same problem... A colorblind option would be nice though I understand the difficulty in redoing all the pallets. However even less saturation in the background would be enormously helpful to start with.

For what it's worth, I have zero problems with bullet visibility.

Seems that it's very few of us who have any difficulty seeing some of the bullets. After some reconsideration I think it actually has more to do with the bullet sprites being similar in size and shape to some of the background details at times. I run into the same difficulty when playing Battle Garegga.