I think we need day/night cycle and in night visibility should be decreased and in water we would see creatures which can flash cool lights, u know like medusas in sea. In day everything would be normal ;)
We also need weather, snowy, windy, rainy. You know, when its snowy or rainy you need get better clothes, when its windy your weak supported platforms can broke. When its rainy you need rooftop to dont get wet and cold. Shark should be stronger because now he isnt too dangerous, with spear you can defeat him in 2 minutes, its not reallistic.And if wind will can break our raft, we would can build some of our raft (for example stairs and pillar) using metal. That will give it resistance for wind! Also foundations could be possible to build with metal what will give it bigger resistance for shark attacks :)
Storms! :D Storm would be very dangerous for us and our raft, if we dont have walls it will throw us out of raft, and shark or pyranhas will kill us.
We need more creatures! Some fishes or birds would be great! And bottles with messages as easter eggs :D
If more creatures, also more of these bad! Multiple shark attacks or something. And if we will kill a shark, new will spawn after few minutes not instantly :)
Of course with more dangers we need more weapons. Bows! Throwable spears!(jawelins)
More crafting recipes, for big bottle from metal scraps and ropes which will be expensive but can store more water like for 3 uses :) Maybe crafting recipe for clothes and cap, rags too! also for arrows to our bows of course :)
Fishing net should catch fishes (rarely!) instead of catching items! They should be separate net for catching items and for catching fishes! Also shark should sometimes try to stole our catched fishes in net.
Mainly, getting food should be harder, harvesting potatoes should be most safe way of getting food, but for example fishing would take more time to get fish (a bit faster if u have lure, for example potato or metal scrap) and killing shark should be good rewarded suicide ;)