As I was reading this book, one of my initial impressions was that he had never read the OZ books, despite brief trivial mentions of Baum's history and some of the inconsequential differences between the film and the book. If he had, some of the discrepancies he blames on Hollywood could have been cleared up as simplifications for script development purposes. The essay goes on for 57 pages presenting a variety of personal anecdotes that are only slightly more interesting than Rushdie's analysis--which brings up a number of thoughts which he neither bothers to offer adequate reasoning for, nor successfully argues the validity of.
Ultimately, Rushdie uses the BFI series as an opportunity to write an otherwise unpublishable short story--essentially the auction of the ruby slippers in a Warren Ellis style dystopia, with unnecessary incestuous themes. It becomes quickly apparent that the essay was used to highlight the oh-so-clever ideas he fools around with in an obscure story which lacked an interesting narrative beyond the briefest moments of strange imagery.
It's a pretentious essay, written by a pretentious author, for pretentious readers. If that's you, enjoy. Otherwise, it isn't worth even the short read that it is.