First things first, I don't remember much of the original, reading it in translation when I was a kid. So whatever discrepancies there are in the series with original (of which, I'm sure, there's aplenty), I can't tell. Judging the first season as "based on something", it's a very decent adventure with distinct characters and a straightforward plot and narrative. I liked the character design and portrayal, and most of the acting too. Scene and gear design is also great, IMO - the Nautilus is sleek and swift, the Dreadnought is heavy and menacing, insides of both are also accordingly delicate and utilitarian. It looks great, and complements the story greatly too.
The main downside, as I see it, is the script - not in terms of storyline but in terms of character relationship dynamics. At times, it's unbelievably cringy and stereotypical, with all the cutout mistrust and disdain for no reason, it's just too teenage and cartoonish for the otherwise realistic-looking settings. I mean, it's obviously fantastical and unreal, but it's at no point deliberately magical or superpower-like or anything. Also the ending is a bit too abrupt and haphazard.
I'm not sure there will be season 2, but season 1 is fairly finalised - with a promise of more, of course, but as an extra, not as a cliffhanger. It's a decent watch for a plain but exciting adventure.