When do creations made by human gain true sentience? When do they gain rights? What happens when these replicants are so advanced that their status as replicant is difficult to impossible to detect?
What makes us human in the first place? How do we know our memories are genuine? Without our experiences and memories, are we just organic robots?
Blade Runner gets a few of common pieces of criticisms:
1. Pacing. It feels slow. This might blow your mind: The movie is only 2 hours. The sequel is about 45 minutes longer. I think this criticism is, frankly, invalid. Plenty of art/indie films get positive points for being contemplative, but this is a detractor from Blade Runner for some reason. Pineapple Express has the exact same run time, Sex and the City 2 is longer.
2. Story and dialog. The movie is hard to understand the first time you watch it if you aren't hearing every word of dialog and processing it. I think this is the most valid criticism, but, again, it's supposed to be a good thing for a movie to challenge you to think, to take in context clues, rather than spoon-feeding you how you should feel like it's a summer blockbuster Marvel movie.
3. The ending. It's not much of one, there isn't a big payoff anywhere. This type of ending is somehow totally fine for art/indie films but "not okay" here. Personally, I think we're supposed to feel like being a Blade Runner is a bit pointless. The ending is unsatisfying on purpose, just like the endings in Disco Elysium.