I'd suggest some more detail about the layout, purposes, and defenses of each area. Are there interesting NPCs to encounter in each area?
More could be done about how they control the island's movement: Are there areas dedicated to that? Are there cultists responsible for maintaining the magic?
How can someone land on the island and what defenses will they encounter?
What sort of doom awaits in the Forest of Death? Do the cultists hold ceremonies at the Tomb of Fallen Jarvin? Is it defended by undead or other horrors? Perhaps Jarvin stole precious relics of the church when he fell from grace: Useless to the cultists, they are believed to have been entombed with him. Go to Comment
I'm afraid no matter what kind of ghost ship is written nowadays, it will always be compared with the one (well two) of the Pirates. Luckily, this is more thant a simple mix of the two, and it has a few extra thoughts. Go to Comment
Unfortunately Disney's Pirate's movies were popular. Otherwise this would be fairly original. Regardless, it still sounds like a lot of fun to play. And sea Quests are rare.
5-Plot Twist Idea: The treasure is there, but what if when the relic is removed from the box/ships hold/ship, Deathwail starts to disintegrate. (keeps the PCs from gorging on treasure)the disintegration could be described as pulling the souls from the walls of the ship into the item. opening up holes in the hull, where they once were. Go to Comment
It has been said that within the mountains (or was it the darklands?) there dwells a fluffy creature of immense cuteness. This creature is so adorable that all who encounter it are filled with joy so great their mortal forms cannot contain it. And they explode. Several magic institutions are desperate to study the creature or better yet capture one to prove the theory of an elemental plane of "D'Awwww".