Dang, this was a really solid jam game! You definitely have a solid base line to build off of if you want to try and take this further and turn it into a full game!
Definitely some areas that need some polishing up, most of which looks like it's already been pointed out in the other comments. I personally couldn't really figure out what I was doing right or wrong in the game. I saw lots of hats on still on the train when the round would end, but then it would tell me I only delivered one package. So maybe a little more description in the How to Play section would have helped?
I also noticed that ammo didn't refresh itself between rounds, which meant I kept starting the next round with empty guns. If that was the intended experience that's totally fine, but it was something that just felt odd to me, and took me a while to actively start reloading my gun when the round was over.
Overall though, fantastic game! Something that feels silly complementing, but that I really liked, was your main menu! You had everything nicely laid out, and the controller diagram helped greatly! Definitely something I should have implemented in my game!
Awesome job!