Greenblatt's studies on Shakespeare on "must reads" for me.  His discussion of the tyrants throughout Shakespeare's writings are thought-provoking in a way that I don't find anywhere else.  I particularly enjoy the discussion of Coriolanus, since that particular play is less performed and discussed than others.  I teach Coriolanus every year and students really love analyzing him so this book will add depth to our conversations around the motivations and thoughts of Caius Martius.  

Greenblatt makes it clear what his political leanings are and whether you agree with him or not, this study of the nature of tyrannical power is one well worth reading.