Shakespeare's story as it is written in his play Macbeth is an important element to understanding the workings and motivations of the characters alive in this novel. How much of the 'back story' are you interested in? Just memories, in snippets or do you prefer longer recollections?
A number of you had suggested early on that a plot summary of Macbeth should be put as a preface to the novel and I argued then, as I do now, NOT knowing Shakespeare's play is not a problem. Fleance doesn't know a lot of what happened and neither does the reader unfamiliar with the play. This reader will discover the 'story of Macbeth' when the key characters learn about their history.
When you read this type of novel, are you irritated by the inclusion of the backstory and just want to get on with the present plot or do you enjoy reading them (provided they are exciting and mine are and will be)