But here's the key that will unlock those deeper layers of significance in the new film: In the original Blade Runner, there are strong indications that Deckard himself was a replicant but didn't know it due to synthetic memory implants. Several visual and narrative clues are present in the various cuts of the first film, and the general consensus is that Deckard is indeed a replicant.
For instance, in Ridley Scott's 1992 Director's Cut of the film, the filmmaker added in the famous “unicorn scene” dream sequence that appeared to confirm the Deckard-as-replicant speculation. Early in the film, Deckard dreams of a unicorn during a drunken reverie. Later, one of Deckard's fellow blade runners, a wigged-out dandy named Gaff (Edward James Olmos), leaves an origami unicorn for Deckard to find. This suggests that Gaff knows Deckard's memories, which means they're implanted, which means he's a 'bot.
Director Ridley Scott later confirmed that was his intent with the unicorn business, telling Wired that revealing Deckard's replicant status is "the whole point of Gaff." Scott continues:
"[Gaff] doesn't like Deckard, and we don't really know why. If you take for granted for a moment that, let's say, Deckard is a Nexus 7, he probably has an unknown life span and therefore is starting to get awfully human. Gaff, at the very end, leaves an origami, which is a piece of silver paper you might find in a cigarette packet, and it's a unicorn. Now, the unicorn in Deckard's daydream tells me that Deckard wouldn't normally talk about such a thing to anyone. If Gaff knew about that, it's Gaff's message to say, 'I've read your file, mate.' ... and therefore Deckard, too, has imagination and even history implanted in his head."
Yet some viewers who work strictly by what's presented in the film still feel there's no definitive answer to the question of whether Deckard is a replicant -- after all, the aforementioned tension is based on the idea that he's a human falling for a replicant, so the debate becomes more ambiguous. This ambiguity is a worth keeping in mind as you're going into 2049.
I'm about to bump up against some nuclear-grade spoilers, and I'll try to be careful, but if you want to go into the new movie totally fresh, you'll want to come back to this page later.