So I imagine if you had more time you might've done these things but:
- When the gun fires, there should be some kind of visual feedback to the player besides the audio
- A brief tutorial (that is skipped on resets) where you pick up a bullet, load it into a gun, and fire it (it's a great mechanic, but because it's unusual, players might wonder why their gun isn't working)
I thought this was pretty cool though. Took me like 5 minutes before I could manage to even hit one of the eyes (they're fast movers), but after I managed to do it once, I was more easily able to replicate it, and so then a few minutes later I got 'em all and triggered the ending.