I like this game, it's really interesting to make the enemies not deal damage to you and how that changes the gameplay from how these kinds of games are normally played.
Some music and sfx would have taken this to a whole new level, that's probably the main piece of feedback I can give really. Even just a sfx for shooting and for getting a kill would have made a massive difference in how it feels I think. But ideally some music and additional sounds would really make it feel awesome.
I think the gameplay gets hectic very fast. I'd be tempted to explore something like having a more structured wave system with like small waves, medium waves and then a big wave/boss wave and then go back to small waves and repeat to try and give it a more interesting difficulty curve if that makes sense.
I know time is super limited in a game jam but I just feel like it's better to receive at least some kind of constructive criticism on what could be better as I personally find that useful, so I hope it's not taken the wrong way at all haha :)