MAY CONTAIN SPOILERS
“The Mysterious Island” is one of Jules Verne's better known novels, and forms a kind of trilogy together with “Twenty Thousand Leagues Under the Sea” and “In Search of the Castaways”. I consider “The Mysterious Island” to be the most boring of the three.
Verne had a tendency to fill his novels with a lot of essay-like digressions on scientific and technical subjects, when not stopped from doing so by his editor, and this makes “The Mysterious Island” a hard read, as we learn in painstaking detail how the castaways on an unknown island somewhere in the Pacific manage to build a thriving little community. In a sense, they are cheating, since a mysterious benefactor (who later turns out to be Captain Nemo from “Twenty Thousand Leagues”) constantly aids them, sometimes with advanced technology unknown when the novel was written.
The novel has a “progressive” slant, the heroes being Americans from the Union side in the Civil War (they actually name the uncharted island after Lincoln), while Nemo turns out to be an Indian prince fighting the British colonial occupation of his country. The virtues of science and technology are extolled, sometimes through Nemo (who pilots a submarine), sometimes through the Yankee engineer Cyrus.
Years ago, I actually read a Marxist analysis of the story, trying to claim it for the far left, which argued that the community created by the Union castaways on Lincoln Island is a form of utopian socialism! I'm not an expert on Verne, but the idea isn't entirely farfetched, since Verne did cooperate with reform socialists and often described “utopian” communities in his novels (he became more pessimistic later).
Personally, I prefer “In Search of the Castaways” of the books in the sort-of-trilogy, but your Vernian mileage may vary…