Otherwise known as "The Dio Novel", Jojo's Over Heaven is one of the two translated Jojo novels, the other being Purple Haze Feedback. However, unlike the other, Over Heaven doesn't end up being a significant addition to the series. Over Heaven takes place during Part 3: Stardust Crusaders, but the perspective is now Dio Brando writing a diary. So what exactly does Dio write about? Well, it's a mixture of him about his life during Part 1, describing his meetings with the priest Pucci that set up the events of Part 6, and describing events currently happening in Part 3. This novel tries its best totie all of these past, present, and future events together, and it works well enough. The problem here is that there's really no new content as a result. If you've read Phantom Blood, Stardust Crusaders, and Stone Ocean, then you're not going to learn much, except for maybe a better explanation of Dio's childhood.
Even though Part 6 was clearly not planned when Araki was writing parts 1 and 3, this book really tries its hardest to connect it. The idea of "going to heaven", a pretty central idea in Part 6, is incessantly repeated. Seriously, it's mentioned every few pages. It gets annoying fast.
Overall, Over Heaven certainly doesn't tarnish the Jojo series, nor does it add much interesting. Still, it's a pretty quick read, so if you're a diehard Jojo fan looking for something to do before Part 4 anime comes out, or if you didn't really "get" part 6, then maybe you'll get some kicks out of this.