I like the island idea and the idea that at night a tide comes in and covers the whole island causing you to have to swim back to a boat or drown.
Amazing idea of having an island with a tide. Exploration is a later developed thing but it is definitely one of the key components of a game like this. I would love to see this game of different species of animals as well as a ecosystems and biomes. Another wonderful idea is to expand the ocean, as in make it more diverse in color with different animals and scary stuff. :)