Having just finished reading the book I thought I'd my two pence worth. I would agree with some of the lower scoring comments made. This isn't a full blown biography of the OS from inception to date, and therefore the title isn't accurate. It is instead an early history of the OS, covering the period pre-OS and how it came into being and its early years up to completion of the first series, looking at the key characters and activity. So if you're looking for how they put together Mastermap, or created the National Grid, this isn't the book for you.
Saying that, I really enjoyed the book, its clearly well researched, and if you're interested in how they went about starting to map the whole country from scratch, without GPS's, aerial photography, satellites and computers to piece it all together, then this is an interesting book. The characters, their drive and vision, the influcence of maps on thinking and thinking about maps and the advancement of our relationship with our country it's fascinating. Although google maps are ubiquitous, on a storm day out on the hills having an OS map in your pocket (and compass) is reassuring. Just spreading one out over the living room floor and exploring the map is fantastic. And this book covers how the OS came about, who we have to thank for the maps we have today. What the map makers had to go through say mapping Scotland lugging the theodolite around with them and up and down hills is pretty astonishing (health and safety would probably prevent us from repeating the feat today). Their aims at times of not just creating a map, but a record of the country.
It is, as the author admits, based on her Masters and PhD work (and why not, she passes on a lot of knowledge), which does show through with the copious notes and references and yes at times the tone of the book wavers in between an academic tone and a popular history tone, however at no point is it unreadable or overly academic and actually is very readable throughout.
So on balance quite a good read. If you're into maps, mapping and OS (and who doesn't love the OS), you'll find this book interesting and informative. If however you're looking for a history of the modern OS, not just early history I'd suggest you look elsewhere.