What exactly was the point of this story, really? Was there one? The characters stay cardboard cutouts, character development is non-existent, and the whole plot is going nowhere. Nemo had at least a reason to take the protagonists on board, his expy Robur just wants to be a dick for being a dick's sake. He shows up in a club in Philadelphia, calls everyone there idiots, and then kidnaps the main characters for a trip in his airship when they laugh at him.
I guess Verne really wanted to write a new 20.000 miles under the Sea but was a bit lost for ideas.