If you're a fan of the television show, you'll enjoy this immensely. Sarah Rees Brennan managed to write a book that had the same eerie and beautiful setting of the show.
This book is a prequel to the show, leading up to Sabrina's dark baptism. There is character growth and some backstory you don't get from the television show that makes the characters even more well-rounded. The relationships between Sabrina and her family are highlighted more, and her relationship with Harvey goes on a bit of a rollercoaster.
Definitely pick this up if you like Sabrina! I'm so glad I did.