pretty cool idea.
i think the physics is a bit weird though. i think a bit of inertia in your character controller would help a lot with the feeling. you probably know this, but way it tends to get stuck on edges. maybe experiment with disabling collision between the player and enemies since that caused some problems. i also think you could tweak the hitboxes a bit (i appear to run off the floor in some places).
also, i think the bullets bounce a little bit weirdly. it looks like you are just multiplying the velocity by -1 when i would expect the velocity to get reflected using the surface normal. I don't use unity but i think this might help, if thats the effect you're going for: https://docs.unity3d.com/ScriptReference/Vector3.Reflect.html
as far as tweaking, i think the player's bullets could move faster.