If you want to know what the writer thought of the film...
F. Paul Wilson is well known to have been, to say the least, dissatisfied with the treatment of his book.
What many people don't know is exactly how much he hated it.
He released a collection of short-stories in the late 80s called "Soft and others" (the original edition is long out of print but it can still be found in used bookstores/online and there is also an electronic edition available for download).
One of the stories is called "Cuts" and it is about an author who sells the rights to his book to Hollywood only to see it butchered by a hack director. So the author takes a particularly gruesome and weirdly-appropriate revenge on the director.
Allow me to quote the introduction to the story:
Another Just Deserts story.
I never would have written this one if not for Dave Schow. We were conversing aimlessly at the 1986 World Fantasy Convention in Providence when he mentioned an anthology he was pitching to the publishers. The title was "Silver Scream" and was to contain horror stories dealing with 'the Hollywood experience.' Dave knew my feelings about the way "The Keep" had been treated on the screen. Would I be interested in contributing? I said most definitely. (See? Business really does get done at these conventions.)
Cuts is probably one of the nastiest stories I've ever written. I wanted to do a toned-down rewrite but Dave threatened me with bodily harm if I touched it. So I didn't.
-F. Paul Wilson
If you like Wilson's stuff or just hated the film and wondered who exactly brought such a horrible piece of crap into existence... you owe it to yourself to read the story. I will warn you... it isn't for the squeamish or faint of heart. I'll put it this way: it could NEVER be filmed.