I got to a point in the game where I was just surviving easily off coconuts beetroots and water and the wood and leaves came from the trees I planted. I became incredibly easy and boring. I think It needs to be more challenging with waves/storms perhaps for example. Just other things that can exhaust your resources and damage the boat. The sharks are also quite easy to fend off. If it was multilayer you could raid other rafts for example. Also there aren't many items. Once you've built everything it becomes quite boring. The chair and table seem pointless. There should be more functional items I think. Also for example if your boat could sink you could have a lifeboat. There could be a bed or many other things which could be used. Maybe the ability to make clothing
Oh also I think if you could upgrade things that would be great! See it would be really interesting if you could survive with friends but then you could build weapons on the raft to attack other rafts for example. Also I do think the shark thing would work better if you had like perhaps sometimes more than one! Then you could feed your captures to the sharks haha. If there were different amount of sharks also it would be less predictable and perhaps if you fed the shark it could leave you alone for longer for example.