Here's the thing about Dawson: he's not only read everything about the period he's talking about, he has digested it. The result is an understanding of what the people and movements mean that he's dealing with unsurpassed. He's dealing with 1500 of Christian history.
Dawson is also a son of the Catholic church and takes her point of view: universality is more important in a church than holiness. As a result he looks at things on one side of that vision as rigorist and sectarian, and on the other side as dissipated and humanitarian (too taken up with merely human concerns, no more). But you have to understand the historian to understand his history with any of them. And once you do, you can figure out how to take what he says.
Dawson is setting forth a Catholic vision, complete with a section of blame for the Eastern Church. It reminds me, because of that, of Vladimir Lossky's The Mystical Theology of the Eastern Church, which does something similar to what Dawson does, only from a different perspective. Both are stimulating books.
Reading Dawson requires a lot of attention, but he rewards attention. I always know when I'm reading Dawson I'll come away with useful insights and a better grasp of the meaning of this or that period of history. I look forward to his clear and steadfast progress through a chapter of explanation. He can be relied on to make a really good point and expand your understanding of what happened, and why.