Aside from writing a formal review, I had some more of my own thoughts on James Hannam's book.
From my point of view, one of the specious arguments levelled against Christianity is that it is anti-science, and only under the influence of naturalism - at least methodological - can science make progress. Of course, this is nonsense - not only have materialistic presuppositions consistently failed to prove true or useful (life at its lowest level turned out not to be simple, the earth turned out to be finely tuned for life, the universe turned out not to be infinitely old ... I could go on) but a significant proportion of science has been, and continues to be, done by people within a theistic framework. Arguably, even when the individual scientists deny this, they unwittingly borrow assumptions about the nature of truth from a non-naturalistic epistemology - science simply can't operate with the postmodern assertions about the nature of truth which dominate other disciplines.
The Dark Ages represent a challenge to this, though. It was an era when progress was limited, we were told, as a result of the unopposed authority of the church. Only with the dawn of the Renaissance, with its more humanistic focus, did we even come close to the heights of classical civilisation once again. Hannam's book tells a different story of the Middle Ages, with accessible and enjoyable style, and shows that the world is actually more subtle than received wisdom would have us think.
Also, even more personally, his book ticked boxes relating to my expectations of a good book. I have long had a gripe about people who write books and don't edit them properly. You really ought to be able to get your ideas across in around 350 pages, in my opinion: more than this in a lot of cases is indulging the author at the expense of the reader. Hannam's text comes in at just under this length. In addition, it has an index, a list of names (important when there are so many bit parts in 1000+ years of history), suggestions for further reading, and a huge source list.
One more thing is the interdisciplinary aspect. Hannam's background is science, and he writes understanding the science side of things. But what he has written is historically lively and, as far as I can tell, accurate. Knowledge is too often fragmented, and a more realistic and coherent picture can be obtained when study joins up different areas.