Setting - Bizarre. The artist warns you beforehand that shit will happen. Bizarrely.
Plot - Consistent.
Art - Unique on its on way. Started as generic shounen art, refined over time. Now people seek to imitate it. Araki has even won prizes because of it.
Characters - Memorable. Most Jojos and villains are well thought.
The only thing I can say against it would be that the manga seems to be made by a ragin homosexual in denial.