The old-school aesthetic is always great, especially that ultra-minimalist Game Boy style. I find it quite charming. I liked having to pick up the harpoon every time you throw it, although it can be a bit tedious; I see you say it may not work this way in the final version, although I find it a very original mechanic. Maybe you could leave it as it is and add another upgrade like a gun that shoots bullets that you don't have to pick up but don't kill in one hit like the harpoon. Just an idea.
I think I've reached the end.
I would love to play a finished version of this game :)