Two stars for the worldbuilding, which kept me reading despite feelings for the main character that wavered between apathy and antipathy. de Bodard's descriptions of the social and political arrangements of the Aztec Empire are really interesting. I wish the magic had been equally interesting, but alas it seems rather D&Dish, all shields and mage sight and magic bolts (albeit fueled by blood). I would have preferred something more numinous.
Part of my frustration was that I went into this expecting a mystery novel, and it really, really isn't; it's epic fantasy, with the mystery just another McGuffin. The fun of a mystery novel, to me, is the feeling that if I were just a little brighter and more focused I could piece together the clues myself, the sense that I'm solving the crime alongside the detective. But that requires the narrative actually give
me clues, and de Bodard isn't interested in that. As an example, there's a scene where the protagonist examines the remains of the deceased, including the knife sheath she left behind. He then later has the realization that the fact that the sheath was designed to be worn on the ankle, rather than on the belt, is an important clue and immediately explains why it's important . . . which is the first we, the reader, realize it's an ankle sheath, because previously it's just described as "an ornate sheath."
The protagonists also had a lot of "ah ha!" moments based on his understanding of how magic worked, which I had to take on faith, because the magic system was never otherwise explained.
I will not be reading the sequels.