This book covers a range of interesting topics, including the nature of being twins, secrets, death, and OCD. Niffenegger is good at capturing people's everyday thoughts and awkward moments in an interesting and insightful way. I was fine with the supernatural elements until toward the end, when an event and its consequences just felt too ridiculous to me. 
 The narrator Bianca Amato did a nice job with the various characters, but I found the voices of Julia and Valentina to be really grating (but probably in character).