Guns feel good to shoot and I love your mines, there's a lot of good juicy satisfaction with your equipment and I like how each gun behaves differently.
I like your enemies! I hope "Maskie" and "Big Boy" aren't placeholder names because cute stuff like that can keep my attention when I'm struggling with how hard your game is (which isn't a bad thing.)
It's not super clear that slow down is a toggle and not something you hold down right click for. I'd definitely prefer the latter given the option.
For twitch games like this where a lot of small objects are moving at high speeds, fidelity is super necessary and my eyes actually hurt after looking at all the crazy flashing that you have happening. Color theory and a more distinct way to tell the background from the foreground can help with this.
Enemies are crazy small and hard to hit with anything that doesn't have 100% accuracy.
On the bugs side of things my mouse kept disappearing which made restarting a pain.
I never used the sprint because to be honest even if it has i-frames it feels like it's just shooting me in the foot. Something more direct like a dash when you hit shift might work better here.