The pacing in the book is a little different than in the first two, but it doesn't feel slow at all. Just different.
I loved the reunion of the A-through-L, September, and Saturday. It was fascinating seeing those three cement their friendship and learn to deal with their feelings about September's absences and their own roles within the friendship.

The new setting on the moon was just enchanting! So original and unlike anything I've ever heard of, but so well-described in a few choice words that I could really imagine the whole scene.

The theme in this one is much deeper than the previous two books. September is dealing with a bigger and more complex heart which she feels she has to restrict to some imagined social standards of grown-up-ness and keep her true heart hidden away.

She says that "if you wear your insides on the outside, people look at you strangely."
I have felt that way my entire life! People always look at me weird when I get excited about something that I love.

To be grownup means "to do your job and mind your work", September thinks. But she learns that maybe being grownup doesn't have to mean hiding your heart behind a stern facade. Maybe it just means getting bigger.
I can't wait for that next book to come out! I could read these books forever!