I finally watched Blade Runner after it sat in my hard drive for two years and I really don't get how it became a classic. Was it the first to explore morality in robots? Was it because of the visual effects? The futuristic world? The unicorn symbolism (which I still don't get btw if anyone wants to explain lol)?
It wasn't the first film, but it was definitely one of the earliest films to really flesh out a sci-fi setting. In particular, it was one of the first films to really properly encapsulate a futuristic dystopia. Plus, it was also based on a fairly famous science fiction novel, "Do Androids Dream of Electric Sheep?" which probably bolstered a bit of its appeal at the time. According to my Dad, he said it was a take on the future that he had never seen before on the widescreen up until that point, especially in that level of detail, which became a huge reason why it was his favorite sci-fi movie for a long time. Plus the main villain was also really interesting and bad-ass, especially his last words before death. Plus, people just like Harrison Ford.
The unicorn symbolism doesn't have a defined meaning since the director never divulged it entirely. Some say it represents fragility, purity, virginity, contrast etc etc to represent Rachel as an android among humans.
That being said, rather than the unicorn individually, the dream itself as a whole probably holds a more literal meaning relative to the script.
This depends on which version you watch since the ending and the unicorn symbolism is the main thing that changes between each of the eight versions, but I'm just gonna assume you watched the Final/Director's Cut.
The most immediate thing you get out of the dream outside of the unicorn symbolism becomes apparent at the end of the movie, where Deckard finds the silver unicorn on the ground that Gaff (the policeman that accompanies Deckard throughout the movie) made and left there. Since the unicorn is only otherwise referenced in Deckard's dream and nowhere else and the fact that Gaff has constantly made silver figures throughout the movie to taunt/reference Deckard, this means that Gaff most likely knew about Deckard's dream, which in turn suggests that Deckard is a replicant. This is strongly suggested, but this interpretation changes between versions of the story as some versions lack parts of these edits.
But yeah, the unicorn symbolism probably has nothing to do with why it's famous considering it's version clusterfuck during it's initial release.
In this day and age, unless you really really like sci-fi, you probably won't like Blade Runner that much cause the script isn't anything to write home about.