This is pretty good! There are a few bugs which you might be aware of, like the monsters pushing the player out of the map if you stand still, but let's ignore those for now.
One thing that you can improve is feedback. When you hit a monster, I want to make sure I hit it and it received damage. You can communicate that to the player by making the monster flash red for example.
A bit of an explanation on controls and what the game is about would be nice. This could either go into the game or in your description.
I would recommend having multiple sound effects for shooting with a slight difference in pitch. Constantly hearing the same sound effect while shooting gets quite annoying.
Good job on your game!