But the murders and motives need not have been changed. I just find it hard to swallow a middle aged woman committing murder just to change bed companion.
And the other murders are almost equally pointless, except as they ruin the life of the daughter, which is the key part. The bitch deserved to suffer. How different is the play in these matters?

Dr. Bill, by focusing on the murder and motives, bed companions, etc. you're just scratching the surface. Did you read either link...either the review or Levy's essay? It's all there. These both provide the depth of subtext, the exploration of the greater forces beneath these acts as depicted in character and allegory going back to the original Greek treatment 2,500 years ago!