personally I think your game is awesome! My suggestion would be to keep the crosshair on at all times. It is only visible when approaching the shop/harpoon-refill section. And so it was a bit harder to aim w/o one xD
Regardless it was a lot of fun and the music was very fitting!! I liked how getting all the turret stations improves the survivability drastically. I lost on my first playthrough but thankfully, the shop's unlock feature was permanent. I don't know if that's intentional or not, but that made a huge difference!
I hope your Ludem Dare Game Jam goes well!