I liked the monsters - they look other worldy, invoke that sort of early doom vibe.
also like the fact you have a health bar, power ups and that you can shoot the incoming projectiles.
Area to improve:
Only could fire in the direction i wanted to if i was pressing the corresponding wasd key - where my mouse was didn't seem to matter, otherwise i would just fire downwards. made it very hard to fight monsters.
More monsters, more chaos, less deadspace and "maze" design (IMO).
Great job though! You could flesh this out to something really fun.