Granville-Barker's prefaces to Shakespeare are highly regarded as the first such written from a theatrical (as opposed to literary) point of view. This approach pays particularly high dividends in dealing with this, one of WS's least appreciated plays. (I am currently appearing in a production of it in NYC -- in a small role.) Jan Kott, in describing "Troilus and Cressida" in the 60's, called it "amazing and modern." Cymbeline, in the 90's, seems strikingly post-modern, and Granville Barker, writing in the 20's, accurately describes features of the play which speak strongly to our highly collage-like contemporary approach to art. Highly recommended (as is the Arden edition of the play itself, probably the most charming of all the Arden editions).