I went for the "health is ammo" as well as the "less health = more damage" idea too with my game! I went with the "kill enemies for more health" route rather then stopping to recharge. I enjoyed how you did it though, slowing down to recharge created a ton of tension and felt really good. The visuals are amazing. It felt really satisfying to line up a shot with multiple enemies or to knock an incoming projectile out of the air.
The only thing I found was that the game would sometimes lag if the pathfinding failed, this could be when I was being chased by the yellow guys and they got stuck outside of a boss gate or if an enemy got stuck in the areas collision.
Overall fun game! Check out mine if you get a chance!