I think there's some potential with this idea. I got over 6000 score before deciding to call it.
Enemies can't hurt you if are moving upwards.
I think a different enemy type would have helped the loop a lot, maybe something with a ranged attack? It also seems like there's no way to get health back.
I like the sprite work you've done, it has a really nice vibe to it!
A few more upgrade types would be nice.
I think with some refinement you can make this into something cool!