What are the differences between the alternative versions of Blade Runner?

Maybe this Wikipedia site is of help. To sum up the most important things:

• 1982 Original workprint (failed in audience tests, not released):

  • no voice over
  • no happy ending
  • no unicorn dream

• 1982 US theatrical release:

  • voice overs
  • happy ending (Deckard and Rachel drive through the countryside)
  • no unicorn dream

• 1982 International release:

  • more violence in certain scenes

• 1992 Director's Cut (not done by Scott, but approved by him):

  • no voice overs
  • no happy ending (Deckard and Rachel just leave Deckard's flat)
  • unicorn dream (suggesting that Deckard could be a replicant)

• 2007 Final Cut (Scott's final version):

  • same content as Director's Cut. Plus new scene Deckard at piano and outside club.
  • many technical improvements

The Wikipedia page referred to gives an exhaustive list of the differences, in terms of deleted scenes. There are indeed many scenes in the Final Cut which were omitted from earlier releases. But this is not really to the point.

The answer to the question is what differences those changes have made to the plot.

The Final Cut (2007) is a very different movie, in terms of plot. Harrison Ford is always hunting for replicants, but never before did the director's real vision emerge. Ford's character is defined by the differences in what he does in those changed scenes. The differences boil down to whether he falls in love with the replicant, Rachael, or not. And whether he, Deckard, is revealled to be a replicant himself.

I originally saw the international edition on its UK release in 1982, and most recently saw the latest version, the Final Cut director's version edited by Ridley Scott, and I was amazed by the difference. The Final Cut is a significantly better movie; and I finally understood the reasons why the director was so unhappy with the 1982 release, which the studio had forced him to release in that form, such that - according to press reports at the time - he had tried to disassociate himself from the movie.

The plot changes made in the Final Cut are all for the better, IMHO, giving real emotional depth to a picture which was, on its original release, little more than a routine Bruce Willis style shoot-em-up. Deckard and Rachael finally become real people, with real motivations and real emotions, in the Final Cut; which is deeply ironic, given that in it they are both depicted, by a very subtle implication in Deckard's case, as not actually being human.

Other than the well known ones, ie. removal of voice over, removal of 'happy ending', inclusion of unicorn from Legend, mapping of Joanna Cassidy's face onto Zhora etc etc, there are a TON of changes that have been made from edit to edit.

I think you'll find all your answers here.

I read that the original movie had a voice over added to it to make things more accessible and the happy ending was tagged on because the studio requested it

The film was meant to have subtle implications on whether Deckard was a repicant and of how deeply replicants were in society - how many of the 'people' in the film are actually replicants.

I have never seen the 'Unicorn version' but I read that this was meant to make the emphasis a little stronger.