Cool game! I like the graphics a lot. Has good music and atmosphere, and a decent variety of enemies and areas. Since it's a demo, I imagine there's even more planned!
My biggest critique would be the combat feels a little unsatisfying at the moment. Maybe more impact or variety to the weapon. The first boss was tough, but when I figured out a good strategy to beat it, it didn't feel as good as it should have.
Nice work, keep it up!