There is much that could be said here, but I will only point out a few things. First, McGrath manages to be thorough, yet not overtly detailed. The author's goal is to examine the entire history, impact, and debates within the Protestant movement. Therefore, his subject is very broad and covers 500 years of history that has spread throughout the world. And yet, McGrath manages to hit all of the major issues and moments in the history of Protestantism and give them the history they deserve.
I particularly enjoyed his look at the Reformation (especially his look at Martin Luther), the Radical Reformation, the Catholic response, theology in America, his look at Pentecostalism and the Charismatic movement, and the English Bible (particularly the King James Version).
One of the dangerous ideas that show up throughout the book is the radical idea of the priesthood of all believers, the imperative of translating Scripture, the clarity of the Bible, and the importance of everyday people to read and interpret the Bible for themselves. When the Reformation proposed this idea, it change the world forever. This legacy continues. Obviously this leads to a number of problems. One of the major problems is the many divisions, factions, and denominations within Protestantism. Yet, despite all of this, Protestantism remains faithful to this idea.
Overall, this is a great book, especially for those interested in the history of the Protestant movement. Though at times it has a certain depth that may be difficult to persons who have never studied the history of the Church or of Protestantism, it remains an important book. For young students of Church History will find a great source here that gives great insight from an excellent historian.