*Every* film is pretendy, no?
Even a romcom chickflick is discussing a made up world, but it's not really asking you to think about it. A thud and blunder James Bond/Jason Bourne whatever invites you to put yourself in the place of the protagonist; a level more involving.
Space opera - most science fiction - is just cowboys and indians in space, or (surprisingly often) even older stories translated - the Odessy, the Aeniad, pirates.
But *good* science fiction (I favour Cambell's definition: it's a science fiction story if it doesn't work if the science isn't there) poses a question 'what if', builds a consistent world, and then drops the protagonist in the middle of it and lets him get on with it.
Blade Runner was taken from (inspired by?) a book called 'Do Androids Dream of Electric Sheep?' by Philip K Dick. That was written in the sixties (so it's as old as you and me
) at a time when thermonuclear extinction was looking a serious likelihood; when the space race was on and no-one had got further than low earth orbit. The hippy thing was still going strong, as was racial separation in the states (and a lot of racial abuse over here). WW2 was a strong recent memory. Dick was living a hand to mouth existence, with his only income from his writing and according to his autobiography, eating cat food (illegal in the states).
And yet he wrote, at that time, a number of very thought provoking books concerning the nature or conciousness, of perception, and of reality... is what I see what really happened, or something that has been implanted in me? Am I really who I think I am? And who tells me what to think?
In 'Do Androids..' he describes a world where artificial people are created to do the more dangerous jobs in society; deliberately made stronger and more resilient than normal humans, but with the same drives and instincts. And a very short lifespan, years rather than decades; they're slaves. And some of them don't want to be... they rebel, and they get hunted down.
But hunting them down is a difficult and dangerous job itself - so what if the hunter is an android himself? And he doesn't know whether he is or not... how are his actions changed by that; what are his thoughts when he starts to wonder about it?
And to a large extent, unusually for Hollywood, Blade Runner got it right. A lot of the draw is from the action sequences; a lot from Ridley Scott's *amazing* vision of LA (apparently, in the 21st century, it rains all the time!); but they're just window dressing on the struggle of the main character. It's a film in which the audience is involved; the outcome is by no means obvious nor the way in which it will be achieved. And like many excellent films, it didn't crash the box office when it was first released but has generated its reputation in the forty year since then.
(I deliberately haven't discussed 2049 to avoid spoilers, but it takes the same themes and enlarges them.)