An interesting book that possibly tries to do too much in too little space. Almost half of the book is about history. The history of the vacuum and of zero. It's interesting in itself but felt at odds with the rest of the book that dealt with more modern scientific theories and conjecture about vacuum states, possible universes and so on. As I was more interested in the latter, the former was a little tedious as I waited to get to the "interesting bits". However, if you are interested in the history, John Barrow gives a very readable account.
The second part was very interesting but heavy going at times. Some theories or hypotheses were explained well, others just wouldn't sink in. You have to be wide awake to get the best out of it or maybe just read the words at face value, without trying to get a full understanding about each subject.
So, a book roughly of two halves, each of which may have warranted a whole book each. I'd certainly like to have read more thorough explanations of many of the ideas about scalar fields, and vacuum energy states. Worth a read but I think it's going to take a second read for me to get the most out of this book.