I was thoroughly bored by the prequel to Queen of Stars, King of Swords, and didn't open this book with much enthusiasm. For most of its length, my opinion didn't change. Rigel sells the elfin Starlands as 'better', but we have to assume that means 'despite the required servitude, second-class status, and people trying to kill you'. It's a lot to swallow.
Duncan spends a lot of the first quarter of the book providing an infodump about the prequel. It's well-handled, but it goes on for a long time. I'd actually have preferred a less-sophisticated but shorter lump of backstory. For those who start the series here, though, it should work well.
Much of the book is a continuation of the theme of the prequel - good-hearted, knows-his-place Rigel will do anything for the beautiful queen. It's so syrupy that it's hard to slog through. Much to my surprise, though, the book ends well - with some genuine pathos and a close that finally caught my interest. My copy contains an excerpt of the next book, Knave of Imps, which answered a key question, but still left me wanting to know more.
So, a slow book with a surprising upturn. It's a strange thing, but after pretty heartily disliking most of the first two books, I could see buying the next.