The first thing I liked about this book was the way that it is organized chronologically rather than alphabetically. This makes it a true (hi)story rather than just a dry gazeteer. There is detailed information about the larger companies and the designers who worked for (or sometimes at odds) with them, but smaller outfits are not forgotten. The links between different organisations and writers are made clear in the body of the text, but I found the "What to Read Next" sections at the end of each larger company's entry particularly helpful in directing me to related articles.
Beyond these admirable details the author draws out overarching trends which affected the industry since 1974, including trends of different sorts and styles of games and periods of boom and bust. I think the author also did well to show sympathy for designers who had a rough ride with certain companies, whilst also showing understanding for the market and corporate forces driving the organisations.
My only criticism is the lack of an index, or at least an alphabetical list of designers and the companies who published their products. I've been reading this pdf on a portable device, and searching takes a long time!
Overall I found this a detailed and engaging guide to the RPG business from its wargame beginnings to the present day, which puts my favourite RPGs into context and has whetted my appetite to explore others.