- 1) We get our first glimpses, and learn of the functioning, of Red Noah.
2) We are given the history of Atlantis and its people.
3) We see Nadia's past, learn more about her as a person, and also learn why she doesn't eat meat.
4) The relationship between Nadia and Jean deepens.
5) We discover when Nadia first learned she could understand animals.
6) We see the ancient factory, including back-up Nautilus ships.
7) If you skip these episodes, it makes no sense how Nadia, Marie, and Jean wound up suddenly in a crashing balloon with Ayerton, Grandis, Hanson, and Sanson.
8) We actually learn the SECRET of the Blue Water (you know, like in the title of the series).
So why is it that people don't like these episodes? It's hard to say. I suppose it has to do with two things: 1) the pace of the plot slows down from where things were heading, and 2) the animation quality drops. First, I don't think the pace slows down all that much. Things still move ahead steadily at a nice clip. The show does become a bit more child-like as it had been in the early episodes, which I feel most of the viewers couldn't stomach. But I had no qualms with that. Second, yes, the animation quality does drop. But it's not as horrible as you think it is. It's not as if the rest of the series is produced with Ghibli-like attention to detail. The animation is passable, and is not like we are watching a bunch of animated stick figures or anything like that.
I read somewhere that Anno denounced these episodes, but he also stated that he like episodes 30 and 31, where a number of the revelations took place. If even he could find something salvageable in these episodes, then so too, should a bunch of over-critical otaku.
I think that anyone who recommends Nadia and then tells people to avoid the "island episodes" is doing a disservice to everyone. The episodes provide new depth to the characters, and also provide a richer plot. Sure, there are throw-away episodes like the singing episode, but overall, there are good things to be found here. For people watching Nadia for the first time, or the tenth, make sure you watch those "island episodes."