Great feedback - The bullets should definitely be a one shot. They're at least something you can dodge too. So I'll be using things like lasers and other dodgeable insta-kills.
My interpretation of the theme was to delve (Fight) the darkness. I thought it would be more interesting to face the fear of darkness and to reveal it for what it is, while showing that it's conquerable - than to directly attack darkness with a weapon.
Sometimes Fighting is just to survive.