Philip K. Dick probably has had more of his works made into movies than any other SF author, but very few of the movies are much good, and most of the few that are aren’t very faithful to what Dick wrote. Dick had a lot of neat ideas that are apparently easy to pitch to preoccupied studio executives, but execution is the rub.
The first hitch is that most Dick movies started out as short stories, and need to be bloated with additional business to turn them into a feature length movie. The novels, on the other hand, are crowded with so many loopy ideas that a lot of them end up on the cutting room floor. It doesn’t help that a lot of Dick’s ideas are easier to get across in written narrative than to show economically on the screen. Blade Runner was a fine movie, but by the time it was done there wasn’t a lot of the original novel left.
The typical Dick protagonist isn’t very heroic: trudging wearily through life, teetering on the edge of insolvency, despair, impending heart attack, marital breakup or mental breakdown. A filmmaker that casts Arnold Schwarznegger as a Dickian protagonist is doomed before he begins.
Dick’s view of man’s relation to God is too central to make an atheist comfortable, and too unorthodox to make a fundamentalist comfortable. Hollywood tends to be allergic to scripts that deal with religious themes in a way that makes a wide swath of the potential viewers uncomfortable.
Dick’s stories seem to attract producers that like the pitch but don’t like the substance. Some of the most Dickian films made were written by other people: the 1980 version of Lathe of Heaven and Donnie Darko.
A Scanner Darkly was rare success as both as a movie and a faithful interpretation of Dick’s novel. The reason it worked was that the filmmaker didn’t need to spend a lot of time fleshing out an unfamiliar future. Scanner was essentially a mainstream novel about the recent past with some minor SF chrome riveted on. The audience didn’t need to be brought up to speed on radioactive dust, the extinction of toads, Mercerism, Penfield mood organs, and the social importance of pet ownership in the post-apocalyptic future, to name some of the Dickian details that didn’t make it into Blade Runner.