It's not often that a Manga makes me literally laughing out loud.
Most comedy Manga were either totally unfunny and boring or just managed to make me blow the air slightly more forceful through my nostrils.
Grand Blue isn't one of those Manga.

The story isn't very special. The art is good but nothing outstanding. Except when one of the characters goes bonkers. Most of the time you'll probably laugh because of the ridiculous over the top depiction of certain emotions.
If you just want to lean back, have a good laugh and not worry about your (shitty) life, then this is the Manga for you.
If you look for anything deeper than just stupid, but very funny, comedy, then don't even bother.
We don't like you anyway.

EDIT: I initially rated this manga an 8 because i only read 6 chapters or so and thought that it would get stale over the time. Turns out, i still laugh my ass of and look forward to every new chapter. Shit's a solid 9, bois.