That's so strange! The game's already programmed so that you can't move when the gun is jammed and the screen is supposed to shake extra hard when the player dies. For the movement, the player loses control but they don't lose momentum immediately so they should drift slightly. As for the screen shake, I'm not sure why that's not working at all. Maybe the web player? I just ask because I had no problems running your game at all in my browser. I'm using Chrome.
I definitely agree with you about the audio, it needs some serious retooling. Being slightly hard of hearing it's easy for me to forget these things, so the input is hugely appreciated!
About the difficulty, I'm going to attribute that mostly to developer blindless lol. I did intend for it to be difficult, but I didn't mean for it to be as hard as many commenters are saying. I'm planning to work on this game more after the jam and add things like a difficulty selection or gradually making the game more difficult. It was just hard for me to figure out how to do that and with limited time I just kinda... threw some levels together before the deadline.
Thank you so much for the feedback, it's very helpful!