Pros:
Great world building
Stayed consistent in his power scale, showed us the power ceiling very early on with admirals/yonko and didnt stray from it. The power progression has also been nice.
Very colorful and diverse characters
Is an author to make you feel for the most retarded things, example: Senior pink.
Cons:
Garbage female design,same face syndrome. Its actually one of the reasons i love hancok, oda himself said that he tried to make her unique and he succeeded. No one in one piece looks like her.
Is a sexist pig,god forbid youre born with a vagina in his manga cause youre either relegated to eye candy/uslessness or both. With some exceptions but even then they arent good enough to write home with.
Inconsistent writting: Tends to have high lows and high highs, especially lately
Fodder overwank: Has this weird fetish of shoving fodder fights and opinions as if we cared about them instead of actual characters we care about. Leads to offpaneling and offscreening any important thing.
Lack of character development for his mcs: This one is a big big stinky doodoo from me, sure some like it and could argue that thats what makes one pieces charm but bruh. Besides robin for a bit and very early one piece nami/chopper, the characters have remained stattic through thick and thin. Makes the story very unenjoyable if your protagonits do not change at all. Luffy from now is the same as luffy from chapter 1. Maybe its just me getting old tho but i do not enjoy this aspect of one piece. The ironic thing tho is that villains tend to be more fleshed out and have character development than the rest. Eg. crocodile, enel's adventures helping out those moon people, moriah,etc.
Overuse of gags: We get it, its their quirk but do you really need to reminds us every single chapter how retarded zoro/luffy are and how perverted sanji is? It really takes from the story/tension to be honest and is not funny at all.
Im sure there is more but there are some that come to mind.