Very fun game!
Shooting from afar is so satisfying. I also really liked the graphics and the sound effects, especially when getting hit. I also liked the detail of enemies destroyed far away making a different explosion sound.
As for improvement opportunities, I think the HUD could use a health bar, or some other graphic that better displays remaining health. Most of the time I didn't notice when I was about to lose during combat, so I wouldn't retreat and try to heal. You could even make the graphic shake and/or flash red whenever the player gets hit to add to the immersion.
Anyway, nice job!