Fantastic score, WOW! That's the beauty of the challenge, I have to stimulate all your instincts ;)
Great suggestion to hold space while shooting. I may add that as a future feature for individuals who want a smoother experience, however my decision for one shot at a time was to add on to the challenge to make the player feel fully emerged as if they're in their last stand, firing away to survive. :P
Have a blessed day!