One of the things I adore about this series is Lily's growth. She started out as unsure, not trusting others, and a bit of a recluse. She's gradually opened up, she has friends (who love her just as she is), she's in a relationship. This book further explores her relationship with Sailor, she has to deal with jealousy and trust. She's stronger for it. I think this book focuses more on Lily's personal life than past books. The mystery is still there (as the "unofficial witchy consultant of the SFPD"), but I felt it was more in the background.
My only disappointment with the book is the ending is abrupt. This particular series has a yearly wait between books. I can take a strong guess where this series might be going.(show spoiler)