I’ve just finished the book and this is my opinion:
First, we can’t forget that Jules Verne is indeed the grandfather of science fiction. In addition, we must look at this book like what it is: notable for its rigorous attention to the laws of physics and science in general as they were understood at the time.
“Journey to the Centre of the Earth” is genuine science fiction from its time, therefore it is a straightforward read that feels to me more like travelling guide
(that gives all the scientific explanations we need to understand the storyline) rather than a common sci-fi book form nowadays.
Even though I had to make a big effort to finish reading this classic, I ended up really enjoying the end (those last two chapters were off the charts).
By the way, I really wish I could have read it in French, I think one of the things that put me off was the type of English that was used in the translation.
Finally, for me the moral of the book was that theories can be rebutted by reality and therefore we should not confuse the two by any means.