The art and music is excellent and it has nice fast paced gameplay.
There we some things that weren't that intuitive when I first started playing, for example, I figured the bat direction would be based on direction from the player character to the mouse cursor position however I actually kind of like it, just took some getting used to. I also like the decisions of where you display the ammo and having the hat based health system is actually a great feature that I'm going to remember.
I did have a random glitch where of of the second blue enemies was stretched out, massive and getting skewed in random directions (probably it's move directions) as it came out of it's spawner I think.