New Moon is the second book in Stephenie Meyer’s Twilight series. You should read the first book, Twilight, before starting New Moon.
As I was reading New Moon, I mentally renamed it as “Bella Goes Emo”. The Twilight series is intended for teenagers and young adults, and I was quite a bit older than that when I started reading it. New Moon is best read when you are the same age (or better yet, younger than) Bella is at the start of the book.
Adults who read this book might find themselves annoyed by Bella’s frequent overreactions to situations. This is especially true for adults who cannot remember how intense life seemed when they were Bella’s age.