A fascinating and educating (and not boring!) look at the life and times of William Shakespeare, or rather, as much as it is possible to know. Greenblatt's research is very thorough and his knowledge of the time period is almost astounding, but I'm holding off on the fifth star for this one because at times it felt a little too much like guessing. Greenblatt comes off pretty sure of himself in the way he makes his (largely unsubstantiated) claims, despite most of them being based on evidence as thin as air.
All in all, I actually preferred Bill Bryson's take on Shakespeare's life. His thesis was: "we don't know jack shit about this guy's life, and people sure are idiots!" Also, much shorter.
But seriously, this book was worth the time and effort, even if I wasn't convinced by its arguments.