The art in this anime is fantastic (especially in non filler episodes, but we'll get to that later). The landscapes are beautiful, and the character design is top notch. I especially like Jean and Captain Nemo's design. The music is another high point in the series with great tracks, some somber and slow, and others bombastic and really add to the grandiose battles.
The plot and characters is where this anime shines the most, the plot instantly grasps you with the mystery of the blue water and takes hold of you for the entire series, constantly hanging it over your head. But the plot really kicks into gear when the main characters are picked up by captain Nemo in the Nautilus. The characters are one of my favorite parts of the show, as to be expected from Anno they are complex and very well written characters. The dynamic between characters is a very strong point as well, Nadia and Nemo's relationship is interesting and fun to watch develop. The Grandis gang is so fun to watch too, but they fumbled the ending with the last minute of the show with Sanson, it's not enough to really ruin the character but it is quite disappointing.
The elephant in the room here when it comes to the negatives of the show is it's filler, which I skipped and will always skip filler no matter the show. However skipping the filler also doesn't feel like a great option because you're left a little confused on how they got to where they are. But I just pressed on and it was fine, but it definitely takes away from the show a little, and is the main contributor to my rating being 9/10 instead of a 10. One more thing I slightly disliked about the anime is I think the ending just moves a tad bit too fast. It's still a really great ending but I wish some things were drawn out a little more. But that being said my complaints are minute, especially compared to the positives of the show which greatly outshine the negatives.
I cannot recommend this anime enough. Especially if you like evangelion, since eva was planned to be a sequel to this show but couldn't attain the rights so they had to reskin it. It's also composed by Shiro SAGISU so you know the soundtrack is great if you've seen eva. I recommend skipping the filler as well, and continue watching until the end because it is well worth the small stumble for that amazing ending.
