September's recommendation: Pavane, by Keith Roberts.
Originally published in the 1960s, this novel was reprinted a few years back as a part of Del Rey's Impact line: "Books That Made the Future." It's an alternate history that takes as its premise the idea that an assassin killed Elizabeth I in 1588. In the chaos that followed, the Spanish Armada met with success, setting in motion the end of the Protestant Reformation.
Contrary to what my subconscious still insists on thinking, though, the novel isn't set in the Renaissance. (I blame the cover, which has tiled images of a portrait of Elizabeth.) It's set in the 20th century, where the Catholic (and only) Church keeps a stranglehold on technological development, so that steam engines are the pinnacle of innovation, and carefully regulated in their uses. The Inquisition is alive and well, stamping out heresy wherever it crops up (as it so often does), and communication over long distances is managed by an insular Guild of Signallers in their chains of semaphore towers.
Pavane has almost an impressionistic feel, as its individual sections go from character to character, telling one peron's story, then another's, then another's. Time steps forward through these tales, moving across several decades, and it takes a while to have any sense of how they fit together, why Roberts chose to tell us the stories of these people. In particular, I wasn't all that engaged by the first segment, wondering to some extent why it was in there, but by the end I understood and saw its place. The novel therefore requires a bit of patience, and a liking for the "slice of life" approach. It pays off at the end, and in retrospect, I think it may be a better way to tell the story of a major world change than the contrived notion that it all revolves around a small group of people at a compressed moment in time. Pavane presents a view more in line with real history: one person does this thing, and then ten years later that one does something else, and bit by bit those pebbles collect into an avalanche.
Where it all goes, ultimately, is a little odd, and I couldn't say with certainty that I buy into it. Despite that, though, I know I enjoyed the book, which is the major criterion for these recommendations. The pull quote on the cover of my copy is from George R. R. Martin, calling it "one of the greatest alternate world stories ever told," and while I haven't made a thorough survey of the subgenre, I can agree with his sentiment.