I really wanted to like this book. I really wanted to be able to give it five stars. But I can't. While there is much to be admired here, this is definitely not the definitive biography of Niels Bohr.
As a previous reviewer hinted, the problem with this book is that it contains far too much quantum physics and not enough Niels Bohr. I am a former high school Physics teacher, and even I had trouble keeping up.
To be sure, there are moments of keen insight. I especially enjoyed reading about Bohr's relationships with his family and with his colleagues. Unfortunately, every time Pais would get me interested in something like that, he would then quickly bring the book to a screeching hault by going back to detail the history of some finer concept of quantum physics.
If you want to read a history of quantum physics with an emphasis on the contributions made by Niels Bohr, then this is the book for you. If, however, you simply want to learn about Niels Bohr the man, you may want to keep shopping.