Batman at 2011-10-18 12:53:47:
The VO changes the tone. The studios put it in to help the slower viewers understand what was going on....
"My mother. I'll tell you about my mother...."
Okay, from memory, as I don't have time to read....
Replicants are starting to think for themselves, and Roy Batty leads the movement. They know they have a limited lifespan. They wish to get this fault removed....
Decker, our hero, goes to where they're made or built, depending on how you look at it, and meets Sean Young (like I said, I'm doing this from memory) and correctly deduces that she's a replicant, although, she doesn't know it.
Decker goes hunting for the four that have escaped, with the help of his former police officer buddy, but he's pretty much on his own, although he runs into current cop Edward James Olmos a few times....
I probably should read it again....
Okay, he takes out two, then he takes out Darryl Hannah, and then chases Batty through the rooftops of the city, they have a knockdown dragout, and a long conversation, and Decker loses!!! But Batty having burned his candle twice as bright, lasts half as long, so he expires....
He makes his report back to his police buddy, and then rides off into the sunset with Sean Young.
Now, depending on whether or not you have the VO, either they lived happily ever after because she was built with no expiration date, OR
They go off into the sunset and Decker knows that he has a limited time, so he needs to make sure he uses it wisely.....
There's more with the resulting dystopia and overcrowding themes, but like I said, I'm doing this from memory. It's actually a very simple detective story when you get down to it.