A fine game, though I don't know if it's as fun as it could be.
First important point: your Mute button does not work properly. It unmutes every time a level starts, ends or when you unpause. The icon doesn't update properly either, so sometimes you have to hit it twice to properly re-mute it, and it does not show the correct red X to indicate it's muted. Very annoying.
Despite what one of your badges suggests, this is not a bullet hell game. It's practically turn-based, considering the rate at which everything travels and the number of bullets you fire. That's actually okay, it makes it more like a classic shooter. However, upgrades really don't seem to pack any oomph, as your massively upgraded level towards the end of the game seems very similar to your piss-poor starting state.
The fact that your fire rate never changes is a bit annoying as well. A slow-paced game is fine, but if you're firing at a pair of enemies shooting missiles at you and you realize you can never break through because you literally don't have enough shots to actually destroy their missiles and reach them, that's pretty disheartening. Also, I don't know if it's a rule or not, but I think it's an inbuilt assumption that eventually, with enough skill and upgrades, you should have a chance at being able to destroy all the enemies on a level. I'm not even sure if that's possible on Level 1 on normal.
I do like that bosses aren't overflowing with hit points. It does feel like you are expected to rely on skill and dodging to fight them, rather than having to learn their patterns perfectly.
All in all, an interesting game, and I like your badges/upgrades/levels system, but I wish it did more, and the game ramped up a bit better.