To summarise my thoughts on this bluntly, it is one of the worst anime I have seen in some time.
The story, all though seems good in theory really is not. With the other elements that should make this a story lacking, this causes it to be absolutely terrible. However, it is less generic than other bad titles I have seen, so gains a slightly higher three for the ingenuity. Its execution and rushed pace is what makes it lacking.
Less art, more badly rendered CGI that feels jolted and out of place. Even for the time it was created, 2001, there was much better
CGI available in western media. With how badly produced it is, I could barely watch it. Mouths moved out of sync with their voices and it feels as if there are frames missing.
The voice acting is pretty terrible, while sound effects feel like they came from stock. Doesn't help that some of these sounds felt like they were used on repeat to make it seem longer (especially the movement of the submarine).
Simply not a one because Amamika's naivety at the beginning used somewhat well later on. However, between the characters being boring and repetitive and bland, there wasn't much room for improvement. Of particular note is that of the parents at the beginning. We as the viewers never learn why they took it upon themselves to restore humanity, which I think is a fatal flaw.
So bad, it's bad. Unlike other bad anime I have watched, I could not gain a single shred of enjoyment from laughing at how bad it was. This was simply cringey, with a few points of "this is mediocre".