I just posted in another thread and saw yours. Very similar to mine. I shall just expand on yours :P
From my play through of this game, it is probably one of the best builder prototypes I have ever played.
A bow would be a great introduction to the game. I would love to see the shark get harder the longer you play as well. Definitely more plants to plant, more fish types with varying hunger levels/poisonous fish that harm you when you eat them. Also a fishing net would be amazing. Either similar to the nets that collect items or a casting net similar to the hook.
I also think a more advanced crafting system would definitely benefit the game. The more you advance, the more stuff should unlock. A more advanced cooking station/water purifier to harvest more at once from a singular station. A furnace to smelt the metal down to ingots for further advanced crafting recipes. Perhaps leading to diving devices as suggested above? Maybe a craft-able cannon to battle the shark (gunpowder could be harvested from barrels)? Upgraded spears/harpoons?
Going along with what I said about more advanced items. As you progress through the game, more advanced materials start drifting in inside the barrels.
Adding durability to items should also be a must since once you create a tool, you can use it indefinitely.
Nighttime/daytime cycles that limits vision as said above. Weather with hot and cold affects the character requiring you to find shade so the reason to have walls and a roof is useful. Bad rain and storms that damage your structures.
With those listed above, seasons could also be added as well as different biomes. This opens up the option to craft clothes based on the environment or something as simple as a rain poncho to help ward of getting cold from the rain. (Furs and such could also be harvested from barrels)
Lastly... This would greatly improve the current game. Add a cooldown to the annoying starving/dehydrating sound. It is probably the biggest annoyance and downside to this game since it spams constantly until you eat or drink.
From what I have seen from this game, it has a HUGE potential. I honestly can't wait to see what future updates hold.