The Last Light of the Sun is set in a slightly altered medevial Europe. Instead of Vikings from Denmark, we read about Erlings from Vinmark. Al-Rassan (Spain) and Sarantium (Byzantium) are both mentioned in this book, so they are set in the same alternate history, but this is completely a stand alone novel, there is no need to be familiar with Kay's other works.
I like this book because it does not romanticize how brutal conditions are during those times. People get killed on raids, sword fighting is nasty, arrows chop down warriors who have surrendered and dropped their weapons. Despite the harsh violence, the characters are compelling and quite likable (Kay has a knack at creating likable heroes). These people live in tough times, yet they love and laugh and dream. It seems authentic, despite the fact Kay allows some magic to slip in - no wizards casting spells or enchanted weapons for barbarians, but there is a nice touch of the faerie.
Much of the story is about Bern Thorkellson, the son of a raider who has forfeited his property and been banished for killing a man in a drunken rage. Because of his father's punishment, Bern has lost status among the Erlings and now exists as a servant. The story opens with young Bern impulsively stealing a fine horse that is supposed to be burned on a chieftains funeral pyre. Of course, the Erlings don't want the chieftain's ghost to haunt them, so they are determined to get the horse back.
A parallel story occurs in Cyngael (Wales, I think) when the household of Brynnfell is assaulted by a raiding party of Erlings. Bad luck for the raiders, it happens that Brynn himself and his men are at the household when the raiders attack. The raid is repelled, but good people die. Even though we have just met these characters, their death is sad.
About a third of the way through the book, with chapters on Bern and Alun (A Cadyri prince), Kay introduces us to the Anglcyn (the English), who are actually the heroes of the novel despite their late introduction. Aeldred is the King, and he is trying to secure his lands against the constant deprivations of the Erlings. We read of his story and his four children. Of course, the stories end up intersecting.
The ending is a bit of letdown. The happy-ever-after wrap up begins without any gigantic climax. Still, this is a novel worth reading. It richly imagines an alternate world, and it is populated with believable, likable characters, both Anglcyn and Erling. For some reason, I seem to have missed reading Kay's Song for Arbonne, so I will have to get to that soon.