Merrick

Rice's prose is still strong, like the previous books in the series. The story is focused on a witch named Merrick, and her relationship with David Talbot. The only Vampire Chronicles element in the book is within a few pages in the beginning and the end.

It does add a bit to the series, because of the ending, which I didn't like very much. Lestat gives his blood to Louis who just tried to kill himself, going against Louis's wishes and making him nearly indestructible. I found Louis suicide befitting with his character, and he has long stopped adding to the series. Armand's resurrection was far more deserving and interesting.

It also introduces what i expect will be an important new character in future stories.

Almost nothing actually happens in the book‘s present timeline. The only significant thing happens at the very end of the book. Most the story is Merrick's backstory, however, it feels flat and boring.
The premise of this book held so much potential, but absolutely none of it is realized. It is emphasized repeatedly how powerful Merrick is; however, she never really does anything much more than reading minds (a trick which even the weakest vampires could achieve with the Mind Gift). Moreover, while Merrick is related to the Mayfairs, she makes it a point not to involve herself with them, so much that is feels like there was no point in even making her a Mayfair.
The scenes with Claudia feel like an afterthought. It does not feel like Louis got any closure in this regard.