For your first Godot game ever, and especially having just learned it THIS WEEK, this is absolutely not bad at all. I'm actually impressed with the lighting effects, I've never actually tried that before and you managed to pull it off extremely well. I'm glad that despite not being able to fit everything in you wanted, you still went ahead and submitted your game. That's half of what game jams are all about, just having the guts to commit to the end! :D
I think, if I could suggest improvements going forward, here are the things I noticed:
- I don't know if it's a bug or unintentional, but the enemies respawn randomly after you kill them. It seems inconsitent, and in a way it doesn't feel fair. If your goal is to overwhelm the player, it might be best to have kind of a "hidden" spawn point where they crawl out of a wall or something, instead of just magically popping back in where the last guy you killed was. Then at least that way it seems like it's more zombies and not just the same zombie being a cheap enemy.
- You would probably be served well when making a shooting game, or any mouse heavy game, to learn how to lock the mouse inside the window. I had a lot of times where I was clicking frantically and accidentally grabbed the titlebar of the window or clicked outside of it, causing me to get killed. Usually you want the player to be able to remain focused on the gameplay and not get dragged out of it or have to focus on specifically not clicking too far in a certain direction. (Of course, then don't forget to give your player a way to get out of the window, even if it's just pressing ESC to quit)
- If you wanted to make the zombies more aggressive, a good way to do that would to make them start approaching the player when shot rather than just having a fixed range of sight. While the second level was hard for me because it was a tight space and they kept respawning, the third level was a cakewalk because I could snipe them from across the map with no response.
I hope you enjoyed your time with the jam and learning Godot, and I hope you stick with it and make more games soon!