C-Beams and Orions Shoulder

Ask most Blade Runner fans to quote Roy Battys famous dying monologue and they'll probably say "like tears in the rain". That's not the way it is seen today, however - it's "like tears in rain".

Based on Philip K Dicks "Do Androids Dream of Electric Sheep?", the movie is legendary amongst Sci-fi fans and has a resurgence with the 30+ year long awaited sequel, Blade Runner 2049.

But the actual line? Perhaps Dekkard should wheel out his trusty Voight-Kampff machine...

Poignant

The speech is remarkable as being regarded as one of the best delivered in any movie, not just science fiction. Rutger Hauer famously improvised the lines he's been given:

I've... seen things you people wouldn't believe...
Attack ships on fire off the shoulder of Orion.
I watched C-Beams glitter in the dark
Near the Tannhäuser Gates.
All those... moments... will be lost in time,
Like tears... in... rain.
Time... to die...

Humanity

The reasons Batty let Deckard live have been discussed at great length, with the general consensus being his final way to demonstrate "what it is to be a real man", i.e. not the machine he'd been struggling to come to terms with throughout the movie.

Replicant

Another theory says that Batty knows Deckard is a replicant himself, and won't kill his own kind out of kinship. But that's just a wild conspiracy theory...