I think you made it a bit too hard. I'd go to the island, harvest some ice and by the time the penguins swarmed me I'd retreat and go back to the shop... but by the time I arrived at the shop all ice melted.
The problem is that the ice was melting too quickly. Still, despite the balance issues I liked the idea of exploring with your ship, finding different islands, fighting foes, that was pretty cool what you managed to make. Maybe if you add more content, like you'd find different shops, or treasures, or you can hire a hitman you can control with WASD on the island (I gotta say it's pretty weird to turn the boat to fire) you could have a commercial game, I think you have a cool idea in your hands if you polish it enough, and one I haven't seen a lot. Great job!