I love the sound effects and screen shake hit effects, nice and juicy! The pixel art in this game is really great as well!
Two pieces of feedback: I think the boss needs to telegraph when they are going to charge. Right now unless you're constantly moving it's really hard to avoid. If you ARE constantly moving it seems like the speed is uncapped, if you hold left or right you'll get up to incredibly speeds and it bugs out the visuals.
Awesome job!