This is the best book I've ever read.
I've read a lot of books, so I don't say that lightly. But I put this at the top of my list and here is why:
The ending: I adored this ending because it was closure. I hold it up for comparison to two particular good series: Boundless, where the right guy got the girl but . . . the really good guy got left out. Bittersweet. And then Delirium, a series I loved but was incredibly disappointed by the ending. I think Cassandra Clare has proven here that it's possible for things to end well for everyone and not be neatly tied up like a fairytale.
The writing: there are so many lines in this book that I think are just profoundly quotable. Maybe it's the 19th century language, but several are just so simple. Check the quotes about this book for a taste. It is not often that you have a book like this be so insightful into the truths of life.
The depth: I have yet to come across a fictional book for young adults that contains so many of the principles this book has. Books by Ted Dekker come close, but they never have quite the appeal that this story offers. Altruistic love, brotherly love, romantic love, propriety, honor, and basically preferring others over oneself - these aren't just good ideas, but they are some of the tenets of my faith. That they are offered to this target group in such packaging makes me amazed. That alone makes the book worth reading.
And now for specifics:
Odds and ends: I love the way we got to know Will even better in flashbacks after his death, seeing him as he aged. I got a shallow sense of Tessa's grief after he died, but that was enough when put in context. I loved the way the romance budded between Cecily and Gabriel. And that whole proposal between Sophie and Gideon was priceless. Throwing Brigit in for a bit of comic relief was wonderful. Magnus Bane was as interesting as Woolsy was intriguing (good guy or bad guy?). Morefield was a crazy bad guy, but I've read crazier, and he was crazy enough for the plot. Which, by the way, took so many turns that I was continually surprised.
And Jem. Well, he was the best part. He admirably fought his circumstances, gave up at the right time, then gave up again to serve, and then after such a long time was rewarded with his heart's desire. Right there is a picture of most people's life of faith. So beautiful.
As a side note, this book is narrated by Daniel Sharman, and he is marvelous.
Everyone should read this book. It is a masterpiece.