Sound in Motion has been described (to me, informally) as a controversial book. How dare someone have the audacity to claim that musicality be taught or constructed intellectually? Right from the beginning McGill addresses (and dismisses) such attitudes that have historically stigmatized the effort to better understand music (and all art) by making a study of it. This alone was a breath of fresh air and gave me a great deal of respect for McGill up front.
The meat of the book is note-grouping, phrasing and a scholarly approach towards interpretation that is highly expressive *because* it is harmonically, historically, and technically informed. The book is broken down into very digestible chapters that read like eloquent discussions one might have in a private lesson. McGill's personal tone is scholarly yet friendly, dryly humorous, and above all conveyed with a sense of warm-heartedness that belies a sincere love of teaching. The difficult or controversial topics such as vibrato or baroque music are handled frankly and honestly without the sense that there must be a "definitive" answer for every piece. Thanks to the organized layout and directness of each topic, it seems possible to use this book as an easy reference. Much of the content of this book will be intuitive to regular performers - many other topics may be intuitive but not yet fully embraced. Personally I've been extremely satisfied with my own playing after applying many of the ideas presented and, by the end of the book, McGill had so earned my trust that I'm going to try to listen to every recommended recording in the Appendix.
I highly recommend this book to every classical musician with at least a basic understanding of music theory. It will take your playing to the next level.