Guy Gavriel Kay, along with George R. R. Martin, are perhaps the best living writers of epic fantasy, and "The Last Light of the Sun" is up to his usual standards. However, this does mean that one has to be in the mood to read epic fantasy to enjoy it.
This is the sort of book where I think one's enjoyment depends greatly on whether you're in the mood to read what it offers.
"The Last Light of the Sun" is not a flexible book or one that fits itself to the reader's mood. It's epic fantasy of a particular style, and insists on being read in that mode. I recommend saving it for when that's what you want to read, and avoiding it if you don't like that sort of thing at all. If you haven't liked any of Kay's previous work, this book won't convert you. For the right mood, though, it's magic, unhampered by its few slight flaws.