To preface this review, I've been playing Granblue Fantasy for nearly three years. The combination of character, plot and world building is what hooked me back then, and genuinely has stayed consistently enjoyable in game in my opinion. I also pretty much never write reviews so sorry in advance!
I understand any adaptation is going to have to take its creative licenses, however there are a few things I think adaptations should be in order to be considered a good adaptation. An adaptation should properly convey the story, themes and characters. While the manga essentially does this, as the story and characters are 100% still
recognizable, it doesn't do a great job imo.
STORY - 6/10
The Gbf manga does something I personally am not a huge fan of in volume 1, which is telling the story in a very "gamey" way. The fight scenes are long and draw from a lot of the mechanical aspects of gbf, while the rest of the story is fast paced and rushed feeling. Volume 2 thankfully feels less "gamey" but diverges in some weird ways from canon in regards to Rackam's backstory? Overall in the first two volumes the pacing just feels inconsistent and the story telling stripped and rushed. The only time it's not is when the story focuses on a new original character that's been inserted into Rackam's backstory.
Art - 6/10
I sure do wish this art didn't have strong ecchi vibes. Ecchi is a legitimate style, but like any style it needs to be matched in content and tone as well. Gbf is a fantasy action/adventure series, without a whole lot of compatible themes or characters to an ecchi style in its vanilla story. The boob and under skirt shots feel awkward at best. Gran's entire design just feels off... I can say is that the monsters and ships look wonderful though.
CHARACTER - 4/10
My biggest gripe overall is 100% with the characterization. Adapting any sort of self insert mc is always difficult, but Gran again, feels off. His characterization would best be described as an unfortunate combination of bland and forceful. I know the english translation of gbf can be pretty different so maybe the manga Gran is more similar to the jp Gran? Gran's big brother energy in the manga seems to have also come at the expense of Rackam's which is an utter shame. Katalina is immediately relegated to comedic relief, (which unfortunately gbf canon does as well, we just get cool knight mom characterization as well). Vryn and Lyria are fine, but they admittedly have very simple characterization at this point in canon anyways.
Seeing as volume 2 is almost entirely about Rackam's characterization, there's a lot to talk about there. We get some pretty interesting expansion on Rackam as an engineer and navigator, some cool scenes with Eugene and more on Rackam's relationship with the Grandcypher. However we also get the new original character that really only seems to exist as, "Rackam's sorta childhood girlfriend who doesn't have any aspirations or drive of her own." (spoilers ahead for Rackam's backstory not covered in manga) She honestly comes across as a weird way to undermine Noa and Rackam's friendship? If she was given any actual personality OR EVEN A NAME that'd be one thing?! But 'nameless childhood friend who supports Rackam and has a promise with him about him flying the Grandcypher' is nearly a carbon copy of his relationship with Noa...
ENJOYMENT - 4/10
The utter lack of world building in the manga, poor or weird characterization, and "gamey" quality really detract from my enjoyment of this manga. Gbf has a pretty simple story that's honestly not that interesting early on, and it's in how you tell that makes or breaks it. The sense of wonder about the world of gbf just isn't present in this manga. The rushed writing and constant nods to the game combined make this a terrible adaptation for someone looking to get into gbf. I'd love to be able to appreciate those nods but they feel shoehorned and take me right out of any immersion I've managed. :/ I wanted to get into Rackam's backstory more in volume 2, but the literally wasted character in it was so frustratingly disappointing it soured the experience.
OVERALL - 4/10
I still love gbf, and I know that makes me both more forgiving and judgemental looking at this manga lol. Are there worse fantasy adventure mangas? Yes. Are there worse game adaptation mangas? Almost certainly. However the gbf is a far cry from what it could have been and that's always just going to be disappointing. If you're looking to get into gbf without playing the mobile game, I'd recommend the anime. If you're looking for a good video game adaptation manga, the LoZ and Eternal Sonata mangas are excellent, and a much better investment of your time.