I imagine that many of Bardfilm's readers will be familiar with Jane Smiley's recasting of King Lear on a farm in Iowa. And imagine most of those that are familiar with it are also aware of its portrayal of the Lear figure and his relationships with his daughters.
In Agatha Christie's Moving Finger (for which, q.v.), one of the character says, about Goneril and Regan, "something must have made them like that" (23). It's not crucial to the plot of Christie's novel, but it's the key point in Smiley's novel.
Larry Cook, our Lear analogue, sexually abused Ginny and Rose, the two oldest of his three daughters, but he never touched Caroline, his youngest. This characterization provides motivation for the Goneril and Regan analogues' rejection of their father and the Cordelia analogue's acceptance of them.
I don't think we're intended to return to Shakespeare's play with any specific accusations against Lear, but the plot of Smiley's novel helps us see that a reading of Goneril and Regan as monstrous might increase Lear's nobility but a more sympathetic reading of the two helps us see Lear's faults and folly more clearly.
I'd just like to call your attention to two scenes. The first is the "division of the kingdom" scene. Notice how understated Caroline's response and Lear's reaction to it are in this vision.
The second scene to notice is near the end of the novel. Instead of a gigantic battle between the forces of England and the forces of France, we have the modern American equivalent: a courtroom.
The book is very difficult—not difficult to read, but difficult to take in and to deal with. But it is also a masterful example of modern Shakespearean fiction.