In absolutely no particular order.
1 - Simon Vance KILLS it as the narrator, as he always does for Kay's work. 
2 - There's this specific style of fantasy that is technically fantasy because it is not set in our world and there's usually a *something*, but where the fantastic elements are slipped in because the story that the author is trying to tell is really a history unbeholden to History and where it's nice to have a little wiggle room with the laws of nature. Ken Liu and Guy Gavriel Kay are my favorite authors writing in this vein, mostly because they both understand how to write conflict without evil. Oh, there are the occasional villains, but war and conflict is the story of two people trying to do what is best and willing to both kill and die for it. (Kay REALLY likes the two honorable albeit not pious men set against each other.) Anyway, it's hit or miss for me as a genre, but lands SO well when it's in the hands of an author who sees real people on the page.
3 - Kay writes religious people extremely well. He understands that history is filled with those who are devoted to their god but are not particularly devout in their actions. And that belief in God shapes people's experiences of the world and the way the think even (especially) if they are not interested in following the rules set down by that god or that god's clergy. Kay GETS it.
4 - Kay is a bit of a stylist; he's one of those authors who can't help but interrupt himself and think about what it is to tell a story. Sometimes he even deigns to give those lines to his characters and, better yet, have them remark on the coincidences of their meetings. It is a bit contrived, I admit. And I love it, I love self-consciousness so much...which, incidentally, is a critical part of understanding my literary tastes. Any book that wants to think more about its own role in being a book and conveying stories to people is a book for me.