I played in browser. I'm not sure if you had actual keyboard controls programmed, (I don't have arrow keys on my keyboard, so if you did, disregard this line), but I didn't care for clicking the placed on GB overlay to control the ship. Otherwise, the main survival mechanic felt fine. Definitely felt some tension as the levels went further, but I'm not sure if it was tension from the enemies themselves, or because I was struggling with the controls.
I agree that the ammo bar made this an interesting take; taking out multiple enemies with one shot felt really good too.
Nice job!