Audrey Niffenegger's first novel. It is quite a debut. I imagine Ms. Niffenegger spent quite some time working on the book - so well-crafted and thought out it is. Time travel, especially non-trivial time travel as a plot device is notoriously difficult. Most of the authors use time traveling paradoxes to create big set pieces, very few are able to use it as the main character development device.
Without giving away too much of the plot, I would have to say that I found the ending somewhat weaker than the beginning and the middle. Either the author or the editors flinched, and decided to offer a saccharine version, with a non-happy, but less than tragic end. The finish also leaves the possibility of a sequel very much alive. Of course, sequels are rather simple to generate when you deal with time-traveling :-)
Of the various small touches I found the loving descriptions of Chicago landmarks, where the author herself lives, particularly endearing. One can feel the smell of snow in the cold air during the winter months. The love story is touching without being overly melodramatic, and the touchstone of the plot is very, very well presented. The task was not an enviable one. Many books have characters traveling through time, but most of the time it is one, at most two, trips. In this book the character moves through the 4th dimension repeatedly, and violently. Moreover, the book covers over 20 years of "normal" time flow. It is gratifying to see the main characters actually grow as people over that period. Again - something most authors of romance and science-fiction cannot do convincingly.
I strongly recommend reading this book, especially you are able to spend a weekend with it in a ski house with a fireplace.