I love this book. I have read it multiple times (I just finished reading it again this morning). It flows well with intense and well written characters. It is heart wrenching, beautiful, intense and an incredible story.
With that said, I have some minor problems with the story that intensify as the book continues. This is the ultimate "mary-sue" story. A Mary Sue is a term in fanfiction for a story that the writer writes about themselves as the heroine. Audrey Niffenegger is a fiery redhead, and an avid reader who works in paper arts and lives in Chicago. The main character Clare is a fiery redhead who loves to read, works in paper arts and lives in Chicago. There is a fine line between writing what you know and writing yourself into a fantasy universe. I love to lose myself in a story, but when the writer writes a story seemingly for only herself, it is hard to become completely enveloped.
A few other qualms. First of all, every copy of this book I have read comes with questions at the end of it for thought. Had I read a teacher's copy and another one didn't include that, this wouldn't be an issue. However I believe Niffenegger wrote these questions herself. Some of them are absurd and way too full of themselves. She penned a fantastic book, but I think it got to her head.
Secondly, there were a lot of holes. For example, Henry thinks on one page about how Clare's friend said something odd to him at the wedding. What she said was never revealed. Generally, Niffenegger was very good about eventually filling in the full story, entire conversations, etc. However there were numerous events which contradicted themselves and a handful of unanswered questions which though minor, were worthy of mention.
Finally, the major one that people who aren't nitpicking will notice is this book's intensity. Everyone loves SO intently. A widower loves his wife and loses his life to her for 30+ years after her death. Clare sits and pines away for her dead husband 50 years, waiting for the promised single moment she gets to see him again. An ex-girlfriend who wasn't that close to begin with (the book says it was a relationship where they both loved to torment the other) intensely loves the protagonist enough to kill herself. There is a time for grieving, then people move on. The characters in this book can't seem to get past the grieving stage.
Despite me airing my grievances with this novel, I highly recommend it. My qualms begin in the final quarter of the book. By that point, you're already too sucked in to put it down.