For such a simple premise I had a ton of fun playing this game. I felt like I had a lot of control over my character's movements with the knockback and it was also just generally fun to do. Only nitpick I can think of is lack of polish but it's a game jam so that's perfectly acceptable. Good stuff!
I think I found some unintentional bugs tho
1. The score counter ticks up when I'm shooting bullets offscreen meaning I'm probably killing bats before they get onscreen.
2. While being midair and having a ceiling above your head if you shoot downwards for some reason it allows you to shoot really fast without a cooldown (now that I think about it that may be intentional but I might as well mention it).
With that said none of these things stopped me from having fun and are nitpicks at best. Just trying to give helpful feedback so you can improve! This was definitely one of the funner games I've played in the jam so far! :)