Cute game!
When facing to the left, the player's bullets spawn behind the player (to the right). I didn't understand what either bar at the top was meant to be. The pools of water are neat, but each one has a barely visible block that prevents you jumping through it. If that's supposed to be there, maybe make it more visually distinct?
I left the game running while typing this up, and half a dozen enemies grouped up on me, but they didn't seem to do anything.
I loved the music, but I thought some sort of audio effect when firing would've been great.