Thanks a lot for your comments and suggestions!
There is indeed some playability: the rock and the sandy platform at the top slides together to the right revealing the skeleton, just as the original set did.
In my eyes the 3 minifigures are not necessarly pirates, but more like seafearing adventurers, treasure hunters (one of them is a lady actually). This is why I omitted pirate flags or a skull pattern on the raft's sail. Also, I didn't feel the need of another faction or enemies as the skeleton/undead guy is a good enough adversary to our heroes. There's also a shark now to fight. :)
Anyways, I've followed many of your advice and done some updates:
- I've changed the gray tiles to tan and dark tan
- The island is now centered on the water plates
- The raft was a bit incomplete indeed, so I've placed a lantern in the front to light the way and added a small weapons/tool rack.
When the 3 figures are on board with their equipment and treasure chest, the raft is pretty well-packed.
Here are the images that tell the Raft Raiders' adventure at the Rocky Reef in this order: Image 1 Image 2 Image 3 Image 4 Image 5 Image 6