The idea is great, the shooting feels nice, the art looks good and it matches the theme.
The only issues are that there is no music and very little sfx, with the sound effects included being rather unpleseant.
The game over menu is good too, but the highscore is based on time, which gives you no reason to kill enemies since you can typically dodge the bullets.
There also arent any healing items, which means that all health is permanently lost. I dont think something like this wouldve been op, especially if combat was rewarded in some way.
I really like it, and all it really needs is a bit of polishing to shine.