I would start off by saying this is a wonderful book, but not one for the uninitiated. John Scalzi's book Old Man's War, its sequel, The Ghost Brigades, and the forthcoming The Last Colony form the trilogy that brings to life the universe that The Sagan Diary is set in. The 'novelette', as it is termed, are the private thoughts of Jane Sagan, one of the principle characters in this series. Topics of her musings run the gambit from love to war and back again, two often divergent ideas which dominate her life in the Colonial Defense Forces.
I've read both the positive and negative reviews from this book and can honestly say that I understand both opinions. This is a niche book in what is (undeservedly) considered a niche genre and one that is very, very different from the aforementioned novels.
If, like me, you have been swept up into the lives of John Perry and Jane Sagan, I truly believe that this book will further cement your love for the characters. Reading Jane's thoughts caused me to reflect on my own life and love, and for a science fiction story to do that it has to be remarkable.
I think John Scalzi did a marvelous job of capturing the essence of who Jane Sagan is, which paves the way for her further adventures with John Perry in Scalzi's next novel, The Last Colony. In spite of all the very enjoyable action and adventure in this series, it is the romantic subplot that helps elevate the books for me and this is a welcome addition to that aspect of the story.
Subterranean Press has put together a very beautiful book with wonderful pencil illustrations by Bob Eggleton.
I highly recommend that you read Old Man's War and the Ghost Brigades, then pick this one up and let it whet your appetite for The Last Colony.