The best thing is simply to refer the reader to Kalliope's wonderful review here:
http://www.goodreads.com/review/show/295775709
For my part, I found the latter portion of the book, discussing Erasmus and More and the imaginary spaces of paradise to be somewhat oversubtle and hard to follow. This, of course, may simply have been due to my own failure of attention. The first part, however, gives a marvelously clear account of the picture, and the reproductions (of the whole and of the details) are simply awesome.