What I felt this needed most was a) better hit feedback for when your attacks, especially the ranged, connect with enemies, all you get is the wet fleshy slap sound, some visual feedback would be good and b) some kind of progression, the enemies gain power over time but as far as I can tell you do not. Almost always, the X-Bullet mode was the safer choice than the horizontal short range attack. The invulnerability period after being hit is very generous and regenerating health was a really good design decision here.
"Story" probably isn't really the right word, but I wouldn't have minded a bit more context on the premise even if it was just some text o on the game page, just like the basics wtf am I and where is this weird gooey meat void I'm in and what are these little freaks I'm killing and why.
I like the pixel art. Was the absence of music in favor of disturbing biological/hospital inspired ambience a deliberate choice?