So if I was looking for a pattern in my reactions to Ross King's writing, I would say that I tend to like his novelized historical books, versus his historical novels. It seems like when his work is based more on a single historical work and how it came to be, he does better than straight fictional stories, even if those stories do include a fair amount of historical research and content. I would put Ex-Libris in the latter category, but that said, I liked this one better than some of the others. I may have read this one, I guessed that I did in my review of Domino (linked above) but I didn't remember then either. Forgettable is probably not a great attribute for a book, but perhaps its apt here.
If this one had a draw back, its that it has so much research and history, that it was, at times, a little hard to follow. There were so many interlacing facts, spread out over a hundred or so years, that it would take a college history class to untangle them, never mind understand them in context. So I did what I assume most readers who aren't 17th century historian would do, I ignored most of it, tried to remember the high points, and assumed that King would help fill in the blanks as we went along, which he obligingly did.
This story is about the power of knowledge, the concentrated power of libraries as fonts of learning, and the various historical powers that struggled to control, ban, censor, and contain that knowledge and keep its power for themselves. It was also a powerful reminder, for me, of why public libraries are the great democratizers, as they have taken that power from the rich and wealthy few that used to hoard it for themselves, and delivered it into the hands of the people.
If you enjoyed King's books on the duomo in Florence, and the frescoes by DaVinci and Michelangelo, you'll enjoy this one too, just not as much.