ill j say what i think, as not being a stan of One Piece and also being a person that doesnt think that One Piece can do no wrong

Art (8/10): Nothing amazing, just ur usual shonen art. Spreads are nice, but every spread in every jump budget shonen manga has abt the same quality. I place the art in between Naruto's and Bleach's.
Story (10/10): This is why ur reading the manga, shits insane. Legit every arc is gold imo except for one of them legit being ass tier and the other just being boring bcs its and exposition arc. Im not gonna say the exposition arc is ass tier tho, its like good ig still. Other than those 2, exery single arc is completely different bcs its a different island
Comedy (8/10): Nothing special, average shonen comedy. Theres just some really good ones at certain points. It does the job, sure it isnt up to comedies like Gintama, but this is a action/adventure series and not an episodic comedy
Characters:
Design (10/10): Each Character is different like completely in both their personality and the way that they look. No character ever looks recycled and each one of them has their own role to play
Development (6/10): I feel as though there is almost no character development. Lets take Luffy, the MC, for instance. If u take him from chapter 1 to chapter 800, he basically the same except hes insanely stronger (the fact that hes much stronger isnt a bad thing). Theres some points where he could have developed i feel like, but it was missed. Something happens right before timeskip that could have easily made him into a much more complex character, but hes basically turned into the same thing except he feels a little more grief. Nico Robin is downgraded from pre to post timeskip. She was legit my favorite character in the crew tied with zoro, but now shes just there. She was really interesting and complex and now she doesnt do anything. Usopp i feel has developed really well. He was certainly a coward and knows that everyone he fights is stronger, but he actually evolves into a person that realizes his own cowardice and improves. Chopper is fine, he starts as the mascot and hes still the mascot. Zoro was a negative parabola imo. He starts out kinda changing into this person who distrusts Luffy to someone who is willing to die for him. Then he devolves into a bloodlust machine that trusts luffy with some alleigances acording to luffy's alliances. Sanji, i swear sanji was a missed oppurtunity. He starts from this perverted woman loving cook, to a perverted woman loving cook who is stronger. Theres this point in a really later arc, in which he gets betrayed by a woman really hard. He could have changed into someone who knows that woman can hurt him, nope. He remains exactly the same.
Villains (9/10): They're all unique and each one has their own motivations. They all have different personalities and such. The way they are beat is also really unique.
Power System (8/10): Average shonen power system but its a bit improved so it isnt insanely broken to one side. Its not HxH level of amazing, but its not autistic like bleach's became in the end.
World Building (10/10): Best world building i have ever seen, they have legit made a whole planet that makes sense and works.
Overall: Manga is a 9.5/10