Readers of this thread might enjoy Dominic Noble's Lost in Adaptation series.

The movie of 'A Scanner Darkly' is the only time anyone did a faithful adaptation of a Phillip K. Dick novel, I reckon. Blade Runner is too different from the novel to even count as an adaptation, really.

I also prefer the film of The Adventures of Baron Munchausen over the book, and Steve Coogan's 'adaptation' of The Life and Opinions of Tristram Shandy didn't even bother to try, and was more about trying to make an unadaptable novel into a movie. I recommend it. (I never did finish the book, but I do remember there being a curse that went on for a full page that was amazing.)