This is largely about the doctrine (Dharma) and conduct (Vinaya) of the first centuries of Buddhism. There's relatively little about Buddhism outside India, for example Japan has just six pages. The tone is fairly academic, for example in its heavy use of Sanskrit. Some of the names of schools of Buddhism have 10 syllables or more, which I found hard to manage.
In talking about the three levels of knowledge (prajna), the author suggests that faith, in the sense of passive belief, "is alien to the Buddhist outlook". Rather, knowledge and wisdom should be developed first through reasoning, then reaching one's own conclusions through reflection, and finally deep assimilation. It's suggested that this is one reason why the Buddha was not in favour of his teachings being compiled into canonical texts. This favoured a multiplicity of doctrine and perhaps makes it difficult to find a common essence in the teaching. As well as the four noble truths and the eightfold path, there are ten precepts and ten fetters to be broken.
The author emphasises that in one form of Buddhist institution, with a given set of practices, it was possible to find people holding different doctrines. Hence orthopraxy (correct practice) was at least as important as orthodoxy (correct doctrine) and one didn't imply the other.
One aspect of Buddhism that can be superficially confusing is the variety of representations in different cultures, e.g. the "laughing Buddha" who is not the historical Buddha but may be identified with Maitreya, who may be considered a Boddhisattva, or a future Buddha.
Overall the book does a good job in explaining, as clearly as possible, a complex and disputed set of ideas while maintaining academic rigour.