"Submarine" really had a different meaning in 1869--it meant
under water. It's impossible to envision what it was like to read this when it first was published.
Really the only bit of suspense is in Antarctica. We in the 21st century are utterly jaded in that respect.
It was O-K. Were I an engineer or scientist I probably would have been more interested in the first half. As it is.... The legend of it beats the reality.