A great game! I know it's from a game jam, but I'll review it apart from the game jam. I love the gameplay; the 'slippery ice' feel of turning the boat is great and I wished that unique feeling was kept for the rest of the game. The upgrades had highly noticeable effects and game progression was good.
I love the weight mechanic of slowing down the boat. Perhaps it should have more of an impact?
Two critiques:
1. There should be some help text to find out what the upgrades do. And other info, I didn't know what the cursed coins did for a long while.
2. The graphics could be better. It's hard to see the boat, tentacles, and other graphics against that background. Even some white outlines could help. It also looks like the game area doesn't match the resolution since the water is floating.
I'd love to replay this with those improvements, and I have some other ideas if you continue to develop this game. It would be nice if we could see the items fall through the water.
I also thought we would see cthulhu at some point, maybe a boss fight? Dunno how that would work. Perhaps for an endgame, you can have the water slowly rise up and the mouse can reach a ladder to escape the well.
Love the game!