I'm catching up on some of the shadow reads I've been picking up and setting down over that last year of getting entangled in all sorts of adventures in Greene-land.
As far as biographies of Graham Greene are concerned, I have found them rather hit or miss so far (as I do most biographies). The problem I see with biographies is any one of them will focus on a certain aspect of Greene's life, leave out other aspects, and authors (quite rightly) try to put their own interpretation on the gaps - not to mention the inconsistencies that Greene has created himself.
Greene is a notoriously difficult character to write a biography about. Research is not only made difficult by Greene's own revisionism and love of practical jokes, but also by the lack of certain information stemming back to his time working for the MI6.
Man of Paradox and A Life in Letters both provide excellent insights behind the scenes the life of Greene. Neither of the two books is a linear biography, but if familiar with the timeline of events in both Greene's personal life and general history, they provide plenty of material that may help to understand the enigma that is Greene.
For my own personal reading experience, shadow reading has not enhanced my appreciation of Greene's writing. He's firmly established himself as one of my favourite writers without the help of secondary literature. If anything, reading more about the man behind the books, it is a testament to his writing abilities that I have not thrown his books against the wall in frustration.