Very interesting take on the theme, i gotta say you made a super versatile gameplay and it's really original for a shooter, i like how you sorta put the enemies and the player on the same level where if you sacrifice your health you risk one hit kills but you can kill ennemies in one hit and dispose of them quickly to not get overwhelmed, its a nice strategy element nicely put within an action gameplay.
Also i really like the NES style music and the visuals, with the really detailed yet simple sprites :) your use of the color palette to comunicate player/enemy health outside of the UI is also awesome !
Had a blast playing this one, Congrats to you :D !!