Killer of Men is the first novel in Christian Cameron's Long War series, which follows Arimnestos, a Greek warrior (and historical figure) during the 5th century BC. It's centered on the Greco-Persian Wars, and this first novel mainly focuses on the Ionian Revolt and the buildup to more famous battles like Marathon.

Christian Cameron is a great storyteller. Everyone has an image of Ancient Greece in their heads - the Acropolis, all white marble, drama and poetry and all that. This novel is set at the very beginning of that 'Classical' Greece, where democracy is just taking hold. Greece is a really interesting setting for me; familiar enough to be recognizable with its gods and cities, and exotic enough to be engaging and fresh. 

The setting being placed further back than your standard Medieval historical fiction is interesting too. Cameron clearly knows his business when it comes to war and battles, and I learned a lot about how the Greeks waged war with such a focus on the phalanx and heavy cavalry being almost nonexistent. It's a huge shift in perspective from your usual 'knight in heavy armor"-focused story.

I've seen some criticism around Cameron's historical novels, that they're a bit formulaic. Now that I've read the William Gold, Tom Swan, and now the first novel of this series, I have to agree to an extent. These books do follow a very general line of: start as low status -> main character involves himself in big events/battles -> gains renown -> participates in big events -> gets humbled -> rebuilds reputation, with pauses in between for self-reflection. It's a formula, but it's a really fun formula. Cameron has found a style that works, and he fits the stories he wants to tell into different settings well.