This is fun! A really interesting take on the theme, and I enjoyed the revolver mechanic itself. It probably took about 30 seconds of messing around smashing buttons and tabbing out to the description for it to click, but I would say it was intuitive enough for most people.
I was really happy to see that you integrated the reloading mechanic with a boss fight who has more health than can be removed with a 6 rounds. I would have liked a melee attack, I don't think it would disrupt or change the gameplay too much, but it was probably the only thing that I felt was truly missing. I was sort of expecting to be able to crouch behind the sandbags / barriers to reload safely from the ranged enemies. However the levels are designed such that I didn't actually need to reload under fire until the very end.
The art is nice and consistent, and the billboarding works for me, and I felt that the music and sfx fit into the whole vibe well.
I thought the level was designed well too, I was able to navigate fine as I just hugged the right hand wall all the way around the level to ensure I didn't miss anything, however some additional clutter wouldn't have been a miss to help players remember where they were if navigating a little more aimlessly.
Overall, a really fun entry, I think the difficulty is about right for a jam game, as is the length; not to long but just enough to cut my teeth on. Thank you!