It's like a Lord of the Rings (the book series), Gone with the Wind, Catcher in the Rye and a million other classics. When they came out they were amazing for their time, so good in fact that a million other writers, directors etc. have "borrowed" from them heavily and improved heavily on the themes introduced by them.
Quite a number of scifi movies borrowed from it: Inception, The Matrix, Ghost in the Shell.
Edit: What's really interesting is reading the book Blade Runner was based on: Do Andriods Dream of Electric Sheep and then watch this movie, they're flip sides of a coin.