Jojo's Bizarre Adventure is a very excellent manga to read. It's unlike any manga that I've ever read, being a multi generational story that focuses on one hero at a time, therefore even if you read one part, it functions as its own story without having to look back onto previous adventures to know what's going on. That being said, it does have its ups and downs
Phantom Blood- A by the book Shōnen
story with a surprising twist at the end and a great villain. It's only flaw is its fast pace and standardized hero.
Battle Tendency- AWESOME Incartnate, the main protagonist. the fast paced comedy, the battle against the nigh invincible Pillar Men, all of which are memorable and the story is some of the best and unique I've ever seen in a manga. It's one of the few stories that perfects the rival story, making you feel sorry when he dies.
Stardust Crusaders- It's above average, its worst moments are the often pointless enemies that pester the heroes and only a truly threatening enemy comes along once in a while. But its those moments that are the most memorable, especially the Daniel D'Arby, J.Geil, Pet Shop and Vanilla Ice fights. It is also significantly longer allowing you to travel along the heroes' journey, and feel sorry when they die. But by far the best part is Jotaro, being a total Badass, if lacking in noticeable traits, and his final fight with Dio, which is some of the best I've ever seen in a manga in its pace, suspense and overall awesomeness. Plus the new system, Stands make the fights very unique since it relies on figuring out how to beat your opponent's powers' flaws rather than overpowering them.
Diamond is Unbreakable- It's average, it's more light hearted than the previous parts and the slice of life stuff aren't too bad since it allows the heroes a breather after a fight. The major flaws is the filler, that Joseph cheated on his wife to force a Joestar protagonist and that we never figure out who the person who saved Josuke was. That being said, the fight with the main villain, who is very unique in his humble ambitions, is epic and well thought out.