Any book must be judged on its own merit, not by the fame or charisma of the author. The standard by which to judge is, of course, the teaching of Scripture. I believe this book is very Scripturally solid.
Pastor Price makes the case for the fact that God has always regulated the activities of his gathered people. He has always prescribed what is to be done and how. He (God) has never left it to chance, or left it up to us to come up with innovations, bright ideas, or anything else of our own invention. He has made all clear in his word, both in the Old Testament and in the New; but as is often the case, clarity does not equal simple (not in the sense of the doctrine falling effortlessly into our hands).
Just realizing that much—that God has always prescribed for his people the activities that they are to engage in when they meet together as the church—is hugely helpful in causing us to stop short and determine to take a serious look at what we are doing, and why. That realization caused Pastor Price to take a step back, and in the fear of the Lord to check it out! He came up not with new, previously unheard of information, but with old information that has by and large been forgotten.
I won't go on about it in this post, but will just leave it at that. There are very important things to know about the doctrine of the singing of the church, and it takes an understanding of God's prescriptions in both the Old Testament and the New to get them. John Price has laid some very important foundational work in his book, I believe. Is he right in every aspect? It's not for me to say for sure, though I do believe from my own studies that he gets his main emphasis right. I'm convinced that we need to be talking about this in our own churches. Because we care about what God wants and has prescribed, we should be open to reconsidering what we do when we gather as the church.