Involuntary time travel +
Multiple child/adult versions of a main character
= very interesting premise
The book is written in first person present tense, which usually doesn't agree with me, but I managed to survive. Niffenegger has an easy and familiar writing style punctuated with big, fancy words that enhanced the literary feel of the novel. The book is 500 pages, so it took me a while to finish, but I was never bored.
I didn't appreciate the graphic sex and profanity in the book, but the R-rated material fit the raw, emotional tone that Niffenegger was striving to achieve. Because of the heavy adult content, I don't know if I'll ever read the book again.
The characters were generally sympathetic. There were occasions where I hated them and their lack of moral scruples. Other times, I admired their constancy and dedication to each other. The book reached me on an emotional level, and I got teary-eyed twice.
It's been two books since I've read Terry Pratchett. Time for a return to Discworld!