This book has quite a number of chapters on the more important Semitic languages, both ancient and modern, and on groups of the less important languages, with detailed and useful information on phonology and grammar of each language. There is also a chapter comparing the sound changes (and grammar changes) of the branches of Semitic. Though not about the individual languages, only the chapter on Modern Aramaic has some important information about the sound changes there, in several dialects. Likewise the book would have benefited from including a chapter on the relationship of Semitic with other branches of Afro-Asiatic. Though to be sure, the relationship is very distant, so few words in common they could be mainly coincidental similarities, and the relationship is proven, or almost proven, mainly by grammatical similarities, especially the similarities in the prefix and suffix conjugations. Those are hardly likely to be similar by chance, though the possibility of borrowing cannot be entirely excluded. But it is at least very likely that Afro-Asiatic is one big family, with the exception of Omotic, which has been related to Afro-Asiatic by error, in my opinion, and is instead an unrelated family. The grammar similarities of Omotic with Afro-Asiatic are too few to be considered as good evidence. So this is an important area of research. But the book has no mention of Semitic being related, or probably related, to other languages.
There is also a useful chapter on the various scripts used for Semitic languages.