I really like the inclusion of the story adds a lot of personality to the game, I also like that the book act's a tutorial while also introducing his character at the same time. I like how the theme was used with the actions of the player character, having been turned into a ghost that's quite fun and having the draining resource of the ectoplasm.
While I like that you have included a couple of different enemies and an increasing difficulty, I wish that the quota increased every round instead and for the enemies to have more attacks like they could also shoot things at you maybe?
The controls are decent but imo i think it would be nice to have the shooting based on the direction of the character and just mapped to one button for easier use and also because sometimes I pressed the wrong button haha. Another way could be based on mouse rotation for more freedom in the direction of fire.
the sprite work is pretty nice and that's there's different ones per enemy type.
However there seems to be an issue where even though I got to the goal in the time limit, it still counted it as a game over, and didn't record my stats at the end and it was all set to 0.
Nice Job overall though! : )