The short version is, it's a fantasy book about bards in a land that has forgotten that language and music are magic. It's split into two parallel stories, one taking place in the pseudo-medieval period of the land and one in the pseudo-Victorian period of the land. There are steam cars and steam trams in the Victorian part, but don't get too excited, that's the only steampunk influence you'll see.
So before i start saying the things i didn't like about it, let me just say it's very good. As usual it is very well written and tells an interesting story, just like all her other books that i've read. However more than any other book of her that i've read so far i think this book leaves the magical aspects of the world mostly unexplained. Even at the end of the book it was fairly clear _what_ had happened but i had very little clue as to the _why_. I'm guessing that maybe people devoted more to high fantasy wouldn't find that so much of a problem, but as someone who would probably consider himself a bit more grounded in SF it bugged me a bit.
I'll put some spoilers here about the particular questions i still had, and then have some more discussion afterward to provide negative spoiler space above the comments.
Spoilers below here! LOTS AND LOTS OF SPOILERS
We know that the old runic language is the key to magic in Belden. We also know Declan, who came from another land, can do magic and doesn't know the runic language or the magic that comes with it, but wants to learn. So why does he never seem to consider teaching Nairn his kind of magic as well as exploring the runic language together?
How _does_ one pass the three trials of Bone Plains? And on that note there's a throwaway line at the beginning where Phelan asks his class which bard did pass them, so we know it's theoretically possible, and also raises the question of who exactly was that bard and what were the circumstances when they did pass them? We know that Nairn failed the first time, though it's not made clear what he should have done instead. However it's not clear what happened the second time they showed up in the books. Did they pass? Or abstain? Or what? The fact that one of the three trials was thrown in as an afterthought after the conflict was resolved definitely confuses the issue.
And most importantly, what is Kelda? Someone mentioned that Nairn would be able to name him, but whether just as Welkin or something more fundamental was never certainly revealed. Is he some ancient bard who failed the three trials? (Proposed at one point in the book but obviously never proven.) Or some kind of avatar of the land or the old magic? Or some kind of personification of death? Some combination of the above? Or something else entirely? The bards in charge seem to be convinced he's dark and dangerous and has it in for them and the kingdom. He certainly acts that way a lot of the time, but then seems find with being "defeated" at the end. So to sum it up, at the end of the book i still didn't know what he was, or what he wanted, or if he even got what he wanted or not. Which makes him a bit of a confusing "villain."
Spoilers above here! LOTS AND LOTS OF SPOILERS!
So the other thing that was weird about this book, which has absolutely nothing to do with Patricia McKillip. I recognized the voice actor right away as soon as i started the Audible book. It took me a couple minutes before i realized it was Marc Vietor, who i mainly know from Glen Cook's "Black Company" series. The Black Company is dark and grim and sarcastic, so listening to the same guy reading something relatively light and fun and lyrical was slightly disjointing.
Just coincidentally however i had the fifth Black Company book lined up right after The Bards of Bone Plain, and i thought it was kind of amusing that i was going to switch between the same author reading completely different styles. However when i started the book i was surprised to discover that they'd switched readers! It makes sense i guess, since the first four books were all narrated by the same person and the fifth book switches to two completely different narrators, but it was still a bit of a shock. Plus there's always a period when a series switches to a new reader where my brain keeps thinking the reader is crap because they do things differently. Sometimes that wears off as i get used to them, and sometimes it turns out the new reader is just crap. Luckily in this case i think i'm leaning towards the first option after listening to about half of the book.