Play report.
The creepy was not entirely successful, but a fun adventure. 
The most memorable moments were the PCs almost escaping the haunted reefs, only to hit a summoned storm that blew them right back in. 
The cold, wind and rain made more of an impression on the players than the creepy happenings, and the frustration of being trapped where they did not want to be, and knowing that bad things were going to continue to happen to them.  It worked equally well on players and characters.
They did not role-play the little girls possession  and crying for help, the howling wolves didn't seem enough out of place on the deserted isle.  After the second phantom the PCs dismissed them as false lures, possibly by sirens.  increased threat of physical violence would have created more fear, as PCs were down to Zero daily powers, and 2 surges each. 
The main problem is that my players and I are rarely serious, and I had forgotten we named the ship the SS Minnow. When the ship broke on the reefs, the captain in despair, planned to go down with the ship, blaming himself for all the misfortunes (true).
One of the PCs ran over and stole his hat. "You won't be needing this *yoink*
The last comic bit was when the PCs finally caught up with the cultists responsible, who were led by a witch.  The wizard PC used his summoned Dretch to knock her out instead of killing her.  The Dretch, which I always describe as "annoying, stinky, and pumpkin shaped demons" was inexplicably bright orange for this adventure.  He knocked her out and then sat on her, oozing various substances, and moaning. 
Anyway, I lean far more to comedy than horror. I should prolly just play to it.
They got her to confess that the cultists were tormenting them to retrieve the statue of Asmodeous the PCs took from the sunken ship.  Since I had not planned for dialog, I missed the chance to play up a the witch angle. and had her just give the relevant information.  Her partner had escaped, and will be seen again. The PCs seized the cultists boat and finally got away.