The central idea of the book, time traveling, is not really an original one, but the narrative angle brings a fresh air in the subject; the writer does a great job not only in addressing time paradoxes in a logically consistent way, but also in presenting time traveling from the point of view -mostly- of the person that doesn't travel in time herself. At the same time the book can be read also as an allegory on couple relationships and how does memory work.
Fine reading, although it wouldn't hurt if it was a bit shorter.