This article is from the Blade Runner FAQ, by Murray Chapmanmuzzle@cs.uq.oz.au with numerous contributions by others.
Ridley Scott made BR in a style called "film noir". Film noir is a
"hardboiled detective" style of story-telling. Perhaps the most famous
example is the Humphrey Bogart movie "The Maltese Falcon" (directed by John
Huston). A trademark of film noir is the voice-overs by the detective,
explaining what he is thinking/doing at the time.
Ridley Scott filmed BR *without* the voice-overs, but due to its poor
reception at a sneak previews, the studio insisted that the voice-overs be
added. Ridley Scott said in an interview on American television that in film
noir, voice-overs sometimes work, and sometimes don't, and they didn't work
"(A)n extensive voice-over was added to help people relate to Harrison Ford's
character and make following the plot easier. (A)fter a draft by novelist-
screenwriter Darryl Ponicsan was discarded, a TV veteran named Roland Kibbee
got the job. As finally written, the voice-over met with universal scorn
from the filmmakers, mostly for what Scott characterized as its 'Irving the
Explainer' quality.... It sounded so tinny and ersatz that, in a curious bit
of film folklore, many members of the team believe to this day that Harrison
Ford, consciously or not, did an uninspired reading of it in the hopes it
wouldn't be used. And when co-writers Fancher and Peoples, now friends, saw
it together, they were so afraid the other had written it that they refrained
from any negative comments until months later." [Source: Los Angeles Times
Magazine, September 13, 1992.]
The ending of the film was also changed by the studio. Scott wanted to end
the film with Deckard and Rachael getting into the elevator, but the studio
decided that the film needed a happier, less ambiguous ending. The aerial
shots used in the 1982 theatrical release were outtakes from Stanley Kubrik's
"The Shining" (which, coincidentally, featured Joe Turkel).
In September 1992, Warner Bros. released "The Director's Cut" of Blade Runner
(BRDC), which eliminated the voice-overs and the happy ending.