Nadia: The Secret of Blue Water - The "Motion Picture"

What? No. These are the only two words, in that order, that can spring from having seen Nadia: Secret of Blue Water: The Motion Picture - incontrovertible evidence that GAiNAX is evil. They're quite capable of making good anime, but that doesn't stop them from being evil.
"Motion picture" probably isn't an accurate description for this. ADV used to use that term to describe pretty much any one shot OVA back in the day, so I'll go with that. One of the biggest clues is the 4:3 ratio.

Two years after the series ended, Nadia and Jean are living apart as Nadia wants to prove that she can live independently. Nadia is working as an assistant reporter at a London newspaper (read: she gets the tea), and the big scoop is that prominent politicians and businessmen from all over the world are evaporating. Turns out that they're robots, despatched by some guy to replace the real aristocrats so that he can slowly take over the world!
Jean finds the daughter of the scientist responsible for the robots washed up on his beach. Her name is Fuzzy, which in Japanese sounds like "Fudgey". Then Nadia is brought into the "web of intrigue".

25 of the first 30 minutes of the film are all recaps of the series. Unfortunately, these repeated scenes are rarely framed by anything to give them context and they are all incredibly poorly chosen. They aren't even shown in chronological order, as something that happened in the 36th episode is shown before something from the 22nd. It's never clear what the writers hoped to achieve with this recap, as it doesn't give a sense of anything from the series.
Vague attempts are made to link the villain, Griegar, to Gargoyle. His organisation simply doesn't make any sense; these aren't really the remnants of Neo-Atlantis.

It gets worse, though; the characterisation is off. Grandis, Sanson & Hanson are money grubbing villains who betray Nadia and Jean. Essentially they have regressed to before the TV series even started. Nothing that they do here is in their characters at all. Nadia and Jean have come much further than this, too, which is why the general premise that they would separate irks. They can't really question their feelings for each other when what happened to them earlier had happened.
Griegar has no real motive, and the link to Gargoyle is non-existent. It's kind of like Gundam Wing's White Fang, but at least that could be explained. Having said all of this, though, the few seconds that the Doctor and Fuzzy get to interact provide the film's only light.

But hey, at least the OP and ED looked nice. The rest of the production is quite ugly, particularly the laziness of the new designs (not by Sadamoto of the series). Everything else about the film sticks in a really bad way; it's hard to believe that the seiyuu came back to record this. Despite the flawed nature of the TV series, overall it was something to be proud of. This ... this is nothing.

I can't consider this as part of the Nadia continuity. It played like a much worse for wear Secret of Mamo and the characterisation ruined it. There was nowhere for these characters to go once the series had been resolved, and thusly they don't go anywhere for the course of this film. Take the epilogue provided by the TV series and run with it. This "movie" never happened, folks ... just move along.