Even though you used Blackthornprod's udemy course, for a first game is actually pretty good. Idk if you made the sprites but they are also good.
I can give you a couple of tips that might make it better.
1. When you start the game it automatically goes to full screen, which is not the worst thing but some people don't always like playing on full screen. (So you should probably add a full screen button instead of automatically going to full screen)
2. The speed of the player and the camera movement are very different, so the player has to wait for the camera to catch up, which camera delay is not bad but when it takes a long time to follow the player is kinda annoying.
3. I think the camera could be little further from the camera.
4. Sometimes there are 0 slimes for 5 seconds and suddenly there comes a wave of 5+ slimes and you can't do anything about it because of as I said the camera follow delay and the camera being to close the the player.
5. The amount of gunshots it takes to kill I slime I think is okay, but as I mentioned before when like 5+ slimes appear It's impossible to kill them fast enough.
Hope this helps :)