This is nice! I like the implementation of slowdown as your health gets lower, it's a nice touch to manage tight situations. I feel like the biggest issue I have with this is the assets. The simple shapes and laboratory floor don't mesh at all, and the floor is a little more distracting with all the noise compared to the simplicity of the shapes. There are also things missing, like when a bullet hits another bullet and destroys it, there is no visual effect, unlike when you get a particle explosion for shooting an enemy.
The addition of enemies fighting amongst themselves is not very conducive for the gameplay, it only hurts the player because they cannot focus on everything happening at once, and then suddenly lose health because a small blue was fighting with a different enemy, and the player was in their line of fire. The idea is really cool, so maybe some tweaks like enemy's speed and rate of fire become slower when fighting with other enemies could help.
I don't know whether this is a bug or intentional, but sometimes after periods of time health pickups cannot be used by the player. If it is intentional, it'd be better you have them destroy or at least communicate that they can't be picked up visually.
The pieces are there, I believe with some revisions and tweaks they can also work together much better.