I see Buffy-books as glorified fanfiction. If you want fanfiction you can get it free and a lot better than these souless novels all over the net. However, this book is different. With painstaking attention to the details of canon and a surprising understanding of Faith's character, Levy has written a suprisingly enjoyable novel.
Written in diary-form, it begins several months before Faith is called as a slayer. We learn about the life she had which was only hinted about in the show. Levy's Faith is much more vulnerable than any version seen previously, but is instantly recognisable. Her voice and behaivour is spot-on.
I tend to find reading fight scenes very boring, but seen here, through Faith's perspective, they get much more interesting. We see her as a girl torn between a longing for security and a need to rebel, torn between love and hatred, and, most of all, between sanity and what she sees insanity.
Tha language of the book is nothing spectacular, but Levy has a reasonable handle on what a teenage girl sounds like. The diary-form does make it fairly unique from other Buffy-products, and the short and pithy enteries make for compulsive reading.
Even if you're not a fan of Faith, I'd reccomend this book. After reading it, I saw her as a much more interesting character, someone who I could feel real sympathy for. All the less important characters are well drawn too - Faith's watcher, her boyfriend, and the rather scary villain.