The Book of Life is the third in the All Souls Trilogy by Deborah Harkness. The first, called A Discovery of Witches, and the second, Shadow of Night, were both good, and this one is a well thought out wrap-up to the trilogy, but it does look like Harkness has left the door open for a follow-up, if that's what she decides to do. I don't have a good sense for how popular this trilogy is, but it looks like is has the tools to be popular, and if there is anything that is keeping it from exploding in the teen market, its probably how smart these books are.
I mentioned in one of the early book's reviews that Harkness cut her teeth on scholarly writing and has number of non-fiction, history books published. She has taken advantage of her research and history skills to lay down a wonderfully complex and fact-based historical backstory for this trilogy. This is peppered with little influences that some of the stories character's have had on history as we know it; its a fun and playful way to help tie the story to the history we understand, and helps to give the story a plausibility by making the reader say, oh yeah, I knew that, and it was this person that influenced it. If this was overdone, it would have been hokey, but it was done with a light touch.
Seems to me that Deborah Harkness has done a fine job or placing herself squarely in the fiction market, in what seems to me to be a very popular genre.
I'll keep my eye peeled for her next book.