I think an island is the perfect setting for a mystery story, especially a murder! It helps to make the story that much more exciting, because you know you can't escape the murderer on a little strip of land. An island also adds a nicer element to the story, in the sense that you dont have to narrow down suspects as much. You know right away, people who arent on the island, arent guilty. To me, being able to narrow down suspects makes the story that much more fun, because i can focus on the story line and the characters much more.