I dig the adventure and concept of the island "existing" on rare occasions. I think the 4th page should be the 2nd instead, I think it would make more sense when reading the module for the first time.
There seems to be a LOT of creatures lurking on the island, between the room descriptions and the encounter table. I don't know if it isn't a bit too many, but there's a wide variety of creatures so that's nice. Though I would have liked to see some "environmental" or weird encounters that are not creature-based.
I loved the encounter table shifting depending on where the characters are. The module seems to have everything you need to play between hooks, rumors, map, encounters and treasures, how to get in and out and all, so good job with that!