I recently saw Ridley Scott's Blade Runner (the 2007 Final Cut version), right after finishing the novel it is based on; Philip K. Dick's Do Androids Dream of Electric Sheep?, and found it an extremely well-made and enjoyable film. It is set in a future Los Angeles, where genetically manufactured replicants (androids in the book), who are impossible to tell from real humans, are used for perilous work in space colonies. Due to past displays of violence, replicants are illegal on Earth, and escaped models are tracked down and "retired" by bounty hunters, the blade runners of the title. The plot centers around a bounty hunter called Rick Deckard (Harrison Ford), who takes on an assignment to retire a group of replicants.
It differs substantially from the book, both by changing the plot and by shifting the focus to different underlying themes, but this actually makes it better and more interesting, since it now works as a complementary development of a similar premise rather than a scene-by-scene adaption for the screen. A major theme in the book only hinted at in the film is that, in a world devastated by nuclear war, the few remaining animals are prized above all else, and the taking of any life is morally revolting. This is contrasted to the systematic killing of androids. What separates humans from androids is the human ability for empathy, but since Deckard's work requires him to shut down his empathy for the androids, what actually makes him any different from them? On the other hand, a primary theme in the film is the replicants' search for a way to extend their short life span, which is a minor point in the book, as well adding implications that Deckard himself is a replicant.
Overall, the film is a magnificent work, perhaps the best part being how perfectly realized it is visually, immersing you in a harrowing future city depicted in a dark, neo-noir style. It's downright fantastic.