Interesting concept but it needs polishing
The player gets surrounded by a tons of enemies as soon as the game starts, I would suggest to make it more like a wave system and the first wave only spawns a few enemies, and the number keeps rising from that point. The game should pause when the shop menus come up (as other people have already mentioned)
I see that you planned on giving each wagon a specific purpose, and having that wagon lost means you lose that feature as well, and I really like that concept. I am sorry that you didn't get time to implement it though.
This could become an amazing game if you are going to make a post jam version