I've written William Peter Blatty's obituary for the Guardian; it's on the website now (link to it here); it should appear in the paper paper soon. The published piece is pretty much as written; there are a couple of extra prepositions (eg: 'from where' he graduated, rather than 'where he graduated') but the body of the story is intact.
And it's a fascinating story. Almost like a piece of literary detection: I was amazed to realise how much the novel Crazy draws together the disparate themes in his work, and it really clarified my own reading of The Exorcist from years ago. Saying audiences were distracted from his themes is not to disparage the film, nor the actors; it says more about audiences that some failed to realise the point, and about Blatty's sincere worry that they didn't.
I would have liked to give a little more time to Exorcist III, at least partly because Blatty had tried to hire Nicol Williamson for The Ninth Configuration, before realising he was wrong for the film. I would have liked to write a bit more about Jason Miller, who plays in both those movies and who seems very obviously a stand-in for Blatty. And about some of the great bits in Ninth Configuration from actors like Scott Wilson, Robert Loggia and Roscoe Browne. When Blake Edwards died I mentioned Gunn, but not Blatty, which I probably should have done.
But what fascinated me most was Blatty's early writing career. The comparison to Perleman has been quoted everywhere, but Blatty was an early part of what I'd see as a very New York kind of satiric farce. You see in movies that feature Zero Mostel or Peter Ustinov. It has the cold war underlying it, and the odd sort of social comedy you see best in Billy Wilder's The Apartment. But mostly I wanted to link Blatty to other comic novelists, guys like Bruce Jay Friedman, Dan Greenburg, Terry Southern, Nathaniel Benchley, even Donald Westlake. There's a very strong stylistic thread running through this (see the film of The Russians Are Coming, The Russians Are Coming, based on Benchley's novel, and compare to John Goldfarb) which deserves more analysis than I could do in an obituary.
I mentioned seeing Catch 22 as an influence on Blatty's Twinkle Twinkle; it seems inescapable to me. It reminds me a bit of William Eastlake's Castle Keep, published a year earlier, and made into a similarly bizarre cult film. I'm not implying plagarism, just that this was what was in the air. Similarly I mentioned Blatty benefited from Rosemary's Baby, but my point about it was lost in another bit of slight editing; I had explained that he benefited because of the success of Ira Levin's novel and Roman Polanski's with respectable audiences. America was ready for the shocker Blatty delivered.