This has potential! I think you should have gone full hotline miami and have the weapons be really lethal, killing the player and the enemies in one shot. It feels like a grind having to shoot so much to kill. I think you should have made a few levels less but polish the experience some more. Like adding a dead man sprite instead of making the enemies disappear and adding a different weapon (even specific to a level without having to code drops and pick ups). Also I think the camera moves too much when rotating with the mouse and that the cursor should be more visible and at a fixed distance from the player or shouldn't be there at all. Keep learning and you'll do well!