Perhaps the best known work based on PKD's stories is the SF classic Blade Runner.
Harrison Ford stars in this classic film of androids and the blade runners--bounty hunters--who chase down and kill the ones who've gone rogue. With amazing graphics and an eerily gripping storyline, this movie changed the way many people thought of the future.
This is not a pretty world. This is a broken world, with violence and deceit. By the end of the novel, Deckard is questioning what makes someone human or not, questioning his own humanity, and questioning whether or not what he's dedicated his life is worth the price he's paying. Without giving too much away, if I had to distill the message of Blade Runner into a few words, I'd say that the movie is ultimately questioning whether or not something manmade (androids) can develop their own form of humanity.
Seeing Blade Runner with a critical eye made me really think about what the movie was saying and what it meant. It was a little shocking for me to see the dirtiness of this world--many science fiction stories show at least a little glitter to the future (see: Star Trek and Star Wars, the two classic SFs on film. Sure, bad things happen--but there isn't the depravity that you see in Blade Runner).
And then I read the novel Blade Runner was based on: Philip K. Dick's Do Androids Dream of Electric Sheep?
I was, to say the least, surprised. There were differences straight off the bat. Deckard is still a bounty hunter, but he's doing it in part to support his wife--a character not present in the movie. And the world is even more decrepit and empty, scarred and hollow--but the book explains why the world has descended into this state.
The main elements are still there: Deckard is chasing rogue androids that are so human-like that they can blend into society. And a lot of the same questions about humanity are there, too.
But...there is something else in the novel. The novel emphasizes that the one solid thing that separates humans from androids is empathy. There's a hint of that in the movie, but in the novel it's remarkably present: the key to humanity, the novel argues, is empathy.
This is a fascinating angle, and one that adds a totally new perspective to the tale. And it's a perspective that's needed. While the movie seems to question whether or not manmade objects can develop humanity, the novel questions where humans find their own humanity after they've lost it. Androids cannot feel empathy--it is the one rule that separates them from humans, and I don't really think PKD cares that much in this novel to explore whether or not an android can evolve.
Instead, we see what Deckard empathizes with. As he ignores his wife more and more, as he discards religion and society, and as he falls more and more into the world of the androids, what he empathizes with--and why--changes.
Because it's not enough, is it? It's not enough to just have empathy. Who we empathize with defines us as a person...as a human.
In the end, it's not really a question of whether or not androids dream of electric sheep. It's about whether or not we do.