The low rating is for the Italian translation work.
The stories are actually quite decent. They're literally "more JoJo", and in the same vein as the main content. There's no big character introspection or original main characters, it's just the Crusaders and 2 more fights on their way to DIO. Fights that would probably fit right in with the rest of the canon events.
The Italian translation, however is very bad. I feel sorry for everyone who's read this version of the book because it's not just full of formatting errors, but also translation errors, and even some Italian errors, and, if all that weren't enough, some deleted paragraphs, and what I can only call "creative changes".
Some examples: there's instances of switching around the speaking character. If it says 花京院, you wouldn't write down Abdul; likewise, Jonathan shouldn't randomly appear and start talking. There's some wild translation mistakes such as rock->storm, wallet->HANDBASKET (I thought I had lost my marbles when I saw Polnareff randomly moaning about his lost handbasket), strange->LEVITATING. There's paragraphs and paragraphs of Jotaro's POV that got changed into a narrator's POV? Some dialogue lines are changed into thought lines and vice-versa, some are broken into 2, making conversations impossible to follow. All of the onomatopoeias are removed, as well as most of the screaming, and while I understand why you'd do this, it still changes a lot of the feel of the book. Almost all Egyptian historical stuff is misnamed (it's Pinedjem in Italian, not PaNeJeM), as are the 2 villains of the first story (Absalom and Michal don't deserve this). All of Jotaro's 'yare yare daze's got translated into the most random stuff.
There's a lot to it and honestly, reading this was a nightmare. Read the Japanese version. Or wait for a fantranslation to pop up somewhere very soon. Really. If you want to spend your 12€ on this book just buy the Japanese one. It's prettier too.