Disappointingly superficial. Evenson mixes hackneyed story craft advice (show, don't tell; setting is important; make character arcs big) with simplistic analysis of the Shakespearean plays to produce a shallow book. It's loaded with talking points (e.g. integrate eternal themes such as love and power, and you'll be writing like Shakespeare in no time!), but the author doesn't really make the effort to show in depth how Shakespeare accomplished his feats or to suggest in detail how you, the reader, might do the same.
It doesn't feel like Evenson carefully mined the Shakespearean texts to discover new ideas for screenwriters; she just shows how Shakespeare occasionally applied basic storytelling techniques. As a beginners guide to screenwriting, this works fine, but don't expect anything deeper.
To the author's credit, the selected film examples are excellent, and there are a few strong chapters (the ones on heroes and villains, and the final two chapters about Shakespeare's writing in general were my favorites).
But in the end, I'd look to the great critics (Bradley, Coelridge, Goddard, Hazlitt, et. al.) to discover the real depth of Shakespeare.