tl;dr The opening chapters are a retcon of book 4. But, the MC is still making really bad choices given his level of information. This is going to be a hard pass for my recommendation.
Much time has passed since my rage fueled review after completing book 4. And, it has been suggested to me that, the series recovers and gets better. If I ever felt the need for validation as to the state of the story at the end of book 4 (in a sacrifice of everything for a spectacle), I received it in the first 2 hours of this book. Many of the plot threads have been smashed. At first I felt like this was a good sign, that things were going to be woven into a new direction. Sadly, this course change had all the elegance of a car crash. So, less than 2 hours in and we have lost the previously built stakes, and thrown out the setting along with the key players. Well okay, so new book new story starting from ground zero. This leads straight into exposition dumping to setup the new setting and players.
Surely there is nothing else this book could do to take me out of wanting to read it… right? Right?! Well the MC proceeds to traumatize people (whom respond in a very meta way). I just, can no longer believe that the MC is a reincarnated person, much less an adult much less again that ruled as a king. The worst thing that happened in book 4, worse even that the unnatural progression of events, was the MC becoming a mindless. child like, vessel to carry the plot and create spectacle. Book 5 is apparently just a continuation, but discarding what should have been salvaged and keeping the rotten bits.
Anyway, you only get my insights into the first 2 hours, for by then all my desire to continue had vanished. If you are new to the series, please consider books 1 and 2, they were lots of fun.