Amazing book.
Perkins' work, though written in 1598, is still extremely relevant today. Each doctrine is introduced by where Protestants and Roman Catholics agree, followed by where they disagree. He then provides the consensus of the Church Fathers with Protestant belief, placing the recently-emerged Protestant faith within the historical church, and various objections from the Roman Catholic side. Having grown up as a Protestant on the missions field in Rome, these objections are still being used against the Protestant faith in this day and age. Perkins' writing is both scholarly, demonstrated by his vast knowledge of the patristics and historical church councils, and approachable, being clear, concise, and direct enough. Furthermore, while Perkins attacks the institution of the Roman Catholic church, he makes clear that we are not to hate our Roman Catholic neighbors, but to endeavor in every way to love them, praying for their salvation - he loves the captive soul while raging against its captor.
Some of my favorite chapters were on Free Will, where Perkins delivers a clear and concise definition and defense of the Reformed understanding of Free Will (10 pgs. give or take), and on Vows, which turned out to have, what I believe to be, very wise thoughts on singleness, marriage, poverty, and life in community.
I would wholeheartedly recommend this book to anyone trying to make sense of the difference between Protestantism and Roman Catholicism. My one criticism is that it is an atomistic approach as opposed to a systemic approach to understanding Roman Catholic theology and practice. For further reading that embraces a systemic approach, I would recommend Leonardo de Chirico's "Same Words, Different Worlds".