Thank for the response
Firstly, the visuals and not being too distracting is a concern of mine. I've actually made many of these things configurable already. Keep in mind that everything I'm showing now is still relatively early. It's been 1 year in development but I imagine it will take a least another year until I'm ready to launch. The screenshake on some of the enemies definitely needs to be toned down. It's something I've implemented quite some time ago and have yet to circle back to cleaning up. I'll take note of the luminosity setting - thinking I can probably just put a semitransparent sheet over the whole background layer and the setting will dial up and down the opacity of said sheet.
Here's an example of the gameplay with the screenshake, debris, and bloom (which gives it that glow) turned off
The gifs are obviously hard to read compared to full screen. As for the game itself, I'll be honest, I'm not an expert shmup player - as I stated in my intro - I'm garden variety indie/retro player and I want to make a shmup for players like myself because I'd pick up something like Gradius and it was just absolutely punishing. What I'll end up making I'm sure won't be a respectable challenge to an experienced player, but that being said - I don't want to disrespect the genre.
Game itself is
-Vertical obviously - why, because I like it better

To me it just plays better - maybe the narrowed screen space is less for your eyes to keep track of. I find that horis are just a little more mentally taxing - it feels more choresome.
-Checkpoints. From my experience with game, I tend to really feel motivated to keep trying if the there's a checkpoint system (as opposed to just being able to credit munch thru stuff). I'd notice I'd spend way more time on an inferior shmup with checkpoints than a superior one without.
-Hitpoints. Mostly driven from using checkpoints. Being 1-hit kill and have the game reset from the checkpoint might mean you spend more time waiting for a respawn vs playing. Been a challenge on finding out what is the right amount of hitpoints to give. In the GIFs I have it currently set to 5, but that might be too much - might bring it in to 3 or even 2, ala ghost 'n goblins
There's more to it - but in terms of hitboxes and whatnot, this is what is relevant.