I have a hard time with stories based on popular tv shows because there is a tendency to alter facts (see Serenity - better days). I was truly impressed with this book. It's starts with the story from the movie Buffy the Vampire Slayer. There are some slight changes but all in all it stayed true to the storyline. Then follows Buffy as she runs away with Pike to Las Vegas. This is the explanation of what happened between the movie and the TV show.
There is even back story about how Giles came to be Buffy's watcher.
The interesting part is that Buffy morphs from Kristy Swanson to Sarah Michelle Gellar. I didn't notice until nearly half way through the book.
All in all it was really well done and I look forward to picking up more.