This was a fun book! To me it has more value than just being the gran daddy of science fiction. I enjoyed the story, and I enjoyed the mystery of trying to figure out who this deep character Nemo was and where he came from. I know other people who read the book get quite bored of the taxonomic description of all the plants and animals, but I didn't, I thought it was fun. 
 Verne seems to treat a little politics and conservationist ideas with a point here and there and then a contradiction later on, but those are definitely not a focus. The focus is definitely Verne's imagination of the mysterious see and Nemo's invention. 
 I did think the ending was abrupt and wasn't really ready for it, but I've read 
 Jules Verne wrote a sequel to this book: L'Ile mysterieuse (The Mysterious Island, 1874), which concludes the stories begun by Twenty Thousand Leagues Under the Sea and In Search of the Castaways, and so I'm interested in following up more plot in those others. 
 I'd recommend this book to any adventure seeker who has at least a slight interest in a historical perspective of the "futuristic," rather than our current understanding of how science really unfolded. Also, I just wanted to mention, even though there are some technological inconstancies with what we now understand, Verne wrote about space exploration, submarines, pressurized deep see diving suits, and taser guns long before any of those things were invented, so at the least he got many things right, and at the most he likely encouraged the invention of these technological advances.