Mild spoilers! it is difficult to talk about the story or characters without saying something...

"What is so hype about Steel Ball Run?" It is a question that people who do not read often wonder the answer.
The part basically gets rid of stands and focuses on stand abilities, so its more the user if fighting than the actual stand. Guns are actually a threat for the first time in the series in a while, and stands are so much weaker that Gyro doesn't even have a stand throughout the part. The fight against the main villain is also very well done, with both sides having interesting abilities. Gyro and Johnny's friendship is also very well done and both are likeable characters.

Andd "Why is Steel Ball Run so good?"
It's one of the most maturely written JoJo story in the entire saga. It's pretty dark, featuring what can be considered the least good JoJo in a moral stance. Unlike previous parts where it's either saving the world or stopping Dio and his minions, Johnny's motivation throughout the story mostly selfish. Some fans might argue that Valentine is more justified in his actions as the antagonist than Johnny is as the main protagonist.
Besides that, the setting really takes advantage the fact that its a race that spans all of the USA in the 19th century. You have various locales and a unique variation of enemies Johnny and Gyro face off against that came all over the world to participate in the Steel Ball Run. I could go on like how Valentine is written as a very likeable villain, how Diego is more than the "i'm evil because i can" guy his original incarnation was, how unique the story behind the stands and the spin are, and all other stuff.
The most important thing is that Araki done a very terrific job rebooting the JoJo universe with SBR. If anything, Part 7 is his magnum opus.

Yep, that's it. I've finished reading the adored and said best part of JoJo's Bizarre Adventure...
What a journey ! I enjoyed every bit of it, from the story (the idea of a horse race through the late 1800s America and the twist of Jesus's corpse being the real objective), characters ( I particularly appreciated Hot Pants and her chemistry with Johnny, but also Sandman who is the absolute madlad, or even minor stand users such as Mr. Blackmore or Ringo) to the entertaining stand fights and the beautiful landscapes shown throughout the race.

I must say I really enjoyed the character of Lucy, a kind of "part 7 Hayato", who endured numerous traumatic experiences, but without giving up. Furthermore, her relationship with her husband was really moving and cute to my mind.

Then Valentine, the perfect villain : behind an evil and selfish goal hides in fact a strong feeling of patriotism, that couldn't nevertheless overcome the thirst for power and control. D4C was a reaaaally op Stand that was absolutely wonderfully used to create entertaining fights with the protagonists.

And finally, oh boy, oh Gyro, such a deep character. He showed us lots of aspects that a JoJo character was expected to embody (a difficult yet moving background, courage, wit, a noble objective, humour, sometimes sadness, and so on. But that was a lot deeper than that, and Gyro was the perfect match for Johnny.

Their relationship just works so well it becomes unreal. Two strangers, different nationalities, different backgrounds yet they are perfectly fit for each other. I fricking loved the jokes/songs moment where Gyro put his whole heart only to be in front of a cold yet amused Johnny, even sometimes adding more to the ridiculous situation.

Johnny was an interesting JoJo to follow. He started the adventure for himself, continued for himself too but couldn't hold back his feelings to intervene when dealing with other characters like Hot Pants or Sandman. Above all, his sincere friendship with Gyro is what made him strong enough to go on on his journey for the corpse's parts.

The protagonist is complex
The main allies are interesting
The villain is believable
Even the throwaway villains are fascinating, especially Ringo Roadagain
The artwork is exceptional (as per usual)
The Stand battles are brilliantly choreographed
And Pulp Fiction reference...

!Yep, like everyone who reads, we can agree to say it was a bizarre yet amazing adventure! A Cripple who likes balls, an Italian executioner, a cross dressing nun, and a Dinosaur man race across America, finding Jesus' Corpse Parts, and fighting the president with neat hair.

Thanks Araki.