Part 6 is overall a pretty mixed bag, its easy to hate on the worst of it but it has many good elements to it as well. Its main problems I found were the forgettable minor antagonists, the DIO retcon, Jolyne's abrupt personality change halfway through and the bad pacing.
Minor antagonists
Lets start with that first thing, pt 6 is not the only part that suffers from this (for some reason pt 3 gets a pass from most in this regard) but its still a big problem regardless, there are 15 minor antagonists in this part, Gwess, Johngali A, Thunder Mcqueen, Foo Fighters, Miraschon, Lang Rangler, Sports Maxx, Guccio, Viviano Westwood, Kenzou, D an G, Miu Miu, Ungalo, Rikiel and Donatello. Out of those there are only a few that stand out in any way, foo fighters becomes an ally and best girl and Donatello had an interesting character for the few chapters we saw him even if his backstory was a direct ripoff of the novel "Holes", Others, like Gwess, Johngali A, Sports Maxx and Rikiel could have been great but just feel like missed chances in the end due to a lack of appearances, backstory or just poor pacing. the rest just feel like nothing or are memorable for small insignificant things, Kenzou: how boring his arc was, Miraschon: her beatdown inspired an execution in danganronpa, Thunder McQueen: Kachow, kill me ect.
DIO and Jolyne
i dont think i have to explain much about why Dio was bad here, nothing that he does in Pucci's memories are in line with his character in pt 3 (which takes place at soon after the latest of the flashbacks) it makes no sense. Jolyne on the other hand isn't often talked about, around the solitary confinement arc her personality goes from bubbly and loud mouthed with a violent side to Jotaro level badass (though she does express slightly more emotion then Jotaro from pt3 which is nice) and she doesn't have those fun quirky moments that made her so charming originaly. I think what Araki was going for here was for her to be hardened by her time in prison which would make sense but the change is so sudden that it just falls apart, we see a bit of an in-between stage around the Marilyn Manson arc but its not enough to justify the complete shift in personality.
Opinions of mine
Ive already explained most of what i had to say about the pacing in the Jolyne section so what I'm going to do here is some things I would have liked to see changed but don't really impact the overall quality.1 I prefered Anasui durring his introduction when he looked more effeminate (not when he's first seen mind you but when his stand if first shown and he talks for the first time). 2 Foof did not need to die that early on, best girl you will be missed. 3 I think that "Giorno may already be in florida" cocktease pissed us all off, It would be idiotic and unsatsfying if he just pulled up with GER during the final fight and bodied Pucci himself but come on, give us something! 4 Why do all the extras look so fucking ugly? please change that shit.
Pt 7
I want to say something real quick about pt 7, going in it has a really slow start but picks up steam tremedously after chapter 33 or so, so don't get dispirited because the first 3rd is really boring, it gets so much better