Very nice game though it's a bit confusing at first with the health damaging me.
The pixel art sprites do look decent, but I think you could have gone for a better color palette. You can find color palettes on lospec or Coolors and many other sites.
Also, some feedback for when hitting enemies and killing them would be a lot better than just making them disappear. Playing any animation is 10 times better than nothing.
To avoid repetitiveness and making it more fun you could maybe put in some powerups or something
Overall a very simple, but fun game when you understand the mechanics.