I've got a few of these "Boxed Sets" and so far this is the best of the bunch.
The "Mysterious Island" is as one might guess a take on "The Island of Doctor Moreau."
I'll probably pass on the Mermaid Isle since the last few scenarios bought featured beautiful evil women. So the guys are paranoid. Maybe make it a standard evil "Sea People" type deal.
There are hooks on the back "cover" inserts for how each isle interacts with the others.
I'm using this in my Pathfinder game in the Atlantis 2nd Age setting. The baddie mad doctor is using an Atlantean artifact from the lost first age called the "Changling Slab," a device very much in the vein of Hawkmoon or the "Doomed Folk" of Elric. The party has to take odd jobs until they get in as crew with the pirates shipping supplies to the isle.
"To go on two legs is very hard. Perhaps four is better, anyway."