I love Jojo. I seriously do. Honestly though, I think Phantom blood is my least favorite story. Not because I hate it, but because Jojo just gets better and better over time. This part did set up a strong foundation for the rest of the series though. It is a story of a wealthy boy, Johnathan Joestar, suddenly having his life turned to hell by his adoptive brother Dio Brando. As they grow into young adulthood, Dio suddenly becomes a vampire and only Jojo can stop him. This part isn't as flashy as the other parts of Jojo, but it does maintain the solid jojo characteristics of "good-of-heart" and honor. Part 1 also does a good job at establishing Araki's credibility as a writer. Araki is able to maintain a unique story atmosphere, while keeping things detailed and appealing. Araki had a similar approach to his first published work, Baoh, but it was not nearly executed as well as in Jojo.
The best thing part 1 does is introduce Dio. Dio is a really amazing character, and VERY IMPORTANT to Jojo. Part 1 is the only time we get to see real character development in Dio, and it gives us the context we need to understand his influence.
This part might be a bit a bit on the bland side, but it is still enjoyable. Seeing characters like Dio do there thing is exciting,and will have you on the edge of your seat sometimes. With this though, the big thing with part 1 is context. Is Phantom Blood a strong start? Not necessarily, but it is a required start. Every part (even later alternate universe parts) are built around the key points of Phantom Blood.It is needed to better understand the rest of the series. It is because of this that it holds a special place in fans' hearts, even if it isn't the best part of the epic manga series.
