I read this in Madrid which added an extra dimension to it, the bulk of it being set in the streets I was walking around every day.
I learned a lot about the Civil War, the social tensions, the different political viewpoints, the machinations of the British, the attempts to keep Spain out of the war and the cost of that for the ordinary people for the next 40 years. I liked the characters, there's lots of plot, lots of excitement and intrigue, but all of it helping to unfold the complexity of the situation. Neither side had a monopoly on righteousness - there is little that's black and white and lots that's grey. I liked the way Sansom put a fairly balanced, though ultimately anti-Franco, argument before us.