This book was really heavy. At first I didn't think so. At first I really felt as if I was putting together pieces of a puzzle, along with the main character, trying to solve a mystery. And then about three quarters of the way through the book, something happened that I really did not expect. I realized in hindsight that the entire book had been foreshadowing the event that I hadn't seen coming at all. This is how foreshadowing should work, in my opinion. It shouldn't spoil the book, but rather, I should be able to look back and see all the signs pointing toward the outcome. This was done expertly.
Metaphors were a major theme in this book as well, and this meant that the book was filled with them. I'm sure I haven't even realized all of them and will put more together as I have more time to think this over.
There are still some humorous elements and running gags like one might expect from Connie Willis, but while some of those have made me laugh and feel lighter after having read them, this one had me in tears. Even as it ended on a fairly uplifting note, I find myself incredibly sad.
I would say this means the author did her job well.