The Van Richten's Guide series is created to be an in-character resource the player can use in order to enjoy a deeper experience within the Ravenloft setting. The Guidebooks are supposed to help the characters understand their enemies in a deep and personal way. It is supposed to help them understand how to confront, deal with, and ultimately kill the supernatural foes they are faced with. It's sort of like a how-to book for adventurers. At least, that is what it is supposed to be.
Van Richten is cursed to write these book because of the violence he inflicted upon a Vistani tribe. While his curse was never directly explained (at least, it was supposed to remain a mystery...creating deeper and deeper mysteries surrounding the whys and hows of Ravenloft), we can see the results of it within the work. He seems to be driven with the singular intent to reveal how to kill every possible enemy in Ravenloft, or at least to lay bare the mysteries without corrupting the adventurer.
This book does not focus on how to kill "The Created" but works as an introductory guide on how to create them. Van Richten acknowledged that most knowledge does corrupt, but he felt free to share the knowledge of their creation rather than go into detail on how to confront them. It seemed like he was trying to tempt and corrupt the PCs rather than do what the series was meant to do. More importantly, the text keeps on breaking character to an extent that it becomes insulting to read. For example, Van Richten referred directly to "Ravenloft" on several occasions even though the actual name of the Demiplane of Dread is unknown to virtually everyone within that place. While some of you may not see that as a big deal, it is vital to keep the mystery alive for the PC and not break the fourth wall.
The book also seemed to only make suggestions to the DM on how to make an overpowered monster for the PCs to fight. To the book's credit, it emphasized the point of making it all fit into a thematic story rather than just making an overpowered juggernaut which would steamroll the PCs.
Overall, this book will not add anything to any PC's experience playing Ravenloft. It's better to avoid it.