this game is really fun, and makes great use of the theme. having the vertical view represent the ammo and the horizontal view represent health was just brilliant and works perfectly.
reloading is rather annoying though, since you have to constantly spam r, which is rather clunky when trying to focus on fighting enemies. i think what would work better is making it so that whenever you press r your ammo constantly reloads without you pressing it, however you can't shoot while do so and you would also be slower. perhaps there could also be a bonus for reloading as little as possible
the score system is also not very good, with it mostly being based on pure luck on how many enemies spawn rather than skill. this could be improved by having it where you gain extra points the less damage you take, as well as the time you take to complete the level.
something that i think would also be cool is if the game had more rogue like elements, with items you can find and with bigger floors that you progress through by going to exits rather than by eliminating every enemy.