Art and audio are really good. Everything comes together to build a specific tone and ambience that I think you managed to pull off. Like the world feels rich even though there's not much to see.
If I were to criticise something about the graphics it's that It's a bit hard to distinguish background from foreground and that the skeletal animations feel a bit stiff. But that's like something really minor.
The shooting and platforming parts of the gameplay could use some work. The character feels heavy and you can die from a few hits. Platforms are too small and you can slide right off them if you aren't careful. If (when) you die, you start right from the beginning of the tower and that felt awful after having trouble with the second enemy. You mitigate this with the healing, but once you ran out of moonlight and the charging spot is taken away, it's practically game over.
Overall I liked it, but found it a bit difficult. It was also cut short, so it left my thirst of vengeance and desire to kill the king unfulfilled. Hope you finish it!
PS: It worked perfectly on Linux (Ubuntu 18.04)