Thank you for the feedback!
I'm glad you pointed those things out. I choose to cut a lot of ideas to avoid scope creep and I agree the game lacks variety. In the future, I plan to add more enemies, bosses and new weapons/movesets. A lot of time went into coding the enemy AI and tweeking the game feel.
On the upgrade department, I also agree. I would say the only ones that are objectivaly good are the health-ups and +1 damage (which is not stackeble). I choose to stick to simple stat increases to avoid bugs and extra work. On the future, I'll probably rework them.
And finally for the light particles, I'll add an option to remove them and I'll try to make pickups more noticeble. I was having major performance issues with Godot's built in lighting system (my PC is also not that good) and had to turn down the visuals a bit. I used additive blending to turn sprites into "fake lights", which made pick-ups kinda of, well, blend with things, making them hard to see.
Edit: I'm also really glad you liked the "choose your color" bit. Maybe it wasn't a waste of time after all...