We just finished watching the third episode of Nautilus on AMC, and I have definitely changed my mind now from where I was after the first 10 minutes of the show...
The story has basically nothing in common with 20,000 Leagues Under the Sea, but after I looked back at a synopsis of the original novel, these episodes are no less believable than Verne's work. The writing is not great, but the setting is, and with the show compressing about 60 years of real world technology it allows the structure of the plot to have a constant threat looming over the crew, much better than the meandering tour the original Nemo took.
For overall feel, the closest comparable show I think to the Nautilus is The Adventures of Brisco County Jr as both are collections of anachronisms held together by comic relief, and a healthy dose of television tropes... so much so that I am probably going to pickup a copy of the Brisco County series, as well as the Nautilus if it comes out.
While this is not a great show, is also not a bad one, and is definitely one to watch to inspire projects set in alternate histories.