This is an interesting one! Inherently kinda paradoxical, and it would have been nice to have some explanation that the player's bullets are essentially special, as they're the only ones that can actually kill individual things without killing everything, including the player.
Ultimately, this winds up playing like a light bullet-hell game where everything has 1 health most of the time, though the little enemies that heal everyone shake that up a bit.
At first I thought it was too easy to get overwhelmed (and if you let enemies pile up it can be very hard to make a dent and get back on top), but it winds up being easy enough most of the time to keep it to one or two enemies on screen simultaneously.