Great aesthetics! The visual style is like a good bow to old school space games. I loved every inch of it!
Controls feel good but I had to change many buttons on my keyboard to find that "shoot" is spacebar :D A tiny tutorial would be a treat (or I'm just blind, sorry, mate).
Interestingly enough I died every time not because of bosses being accurate (dodging is easy). I died because ammo is very scarce. Every. Single. Time. Which is very cool and creepy because it gives you a feeling of predetermined hopelessness: "You can't kill them all, you can't defend it".
(or again I might have just missed "reload" button and the "reload" button I found restarts the whole round).
If that's what your game means to be, very cool! I wish you made a story around that. Your potential is great!