I tried the demo and first of all I have to say I love the idea for the game and I can't wait for the full version!
I agree with another commenter that the thirst/hunger meters drain way too quickly, which limits us from exploring the island. I constantly had to keep eating coconuts or return to the campfire in the cave to sleep.
Also, there are no settings and the game doesn't show you controls (how to open the inventory, how to go back to the main menu, etc.). And like another person mentioned, after I slept and woke up, the UI was not visible and I couldn't see the hunger/thirst/sleep meters and controls. I didn't know how to fix this so I had to exit the game. When I entered again and tried to continue, my progress didn't save so I had to play all over again.
I'll try to play more later and hopefully encounter one of the other characters.