The characters change and the tone of the book is much different in a good way. It's still about friendship and the magic of girlfriends, but is more mature. A great read and a great conclusion to a wonderful story.
The Sisterhood Series by Ann Brashares (The Sisterhood of the Traveling Pants The Second Summer of the Sisterhood Girls in Pants: The Third Summer of the Sisterhood Forever in Blue: The Fourth Summer of the Sisterhood and Sisterhood Everlasting
Sisterhood of the Traveling Pants Series. I don't know why these books have such a bad rep they are absolutely amazing and some of my favorite books of all time. I love this series. Also I absolutely bawled my eyes out during Sisterhood Everlasting.