I’ve been waiting longer than most for George R.R. Martin to finish the A Song of Fire and Ice series: I read the first book when it was newly published in paperback in 1997. Fire and Blood is a new addition to the series, but it is a prequel and does not advance the plot at all. This book is a history of the first half of the three hundred–year reign of the Targaryen dynasty, the dragon riders who conquered Westeros with their firebreathing dragons. The Game of Thrones series takes place fifteen years after the last Targaryen king was deposed.
Instead of a standard novel told from multiple viewpoints, Fire and Blood purports to be a history assembled by a scholar from a variety of sources, decades after the events recounted. As such, it is much drier than the novels and less enjoyable. It fleshes out characters and events oft alluded to in the novels. The Targaryens are a nasty, backbiting lot. They are literally inbred, frequently marrying brother to sister. Different factions feud over succession; civil wars are fought; alliances are made and lives are broken.
This book was once dubbed the GRRMarillion; I would recommend it mainly to completists.