Regardless of box office receipts - is it not the most accessible movie? Concerned that my gf, who likes SciFi, may not like 3 hours of slow burning SciFi...
The scifi isn't the "problem" with BR2049. Well, actually it is, because it creates the expectation of the sort of scifi film people tend to expect. The big questions and mystery in the film don't matter, it's more a thoughtful contemplation sort of film. A character study with some (barely) exciting bits, there's tension but it's more about the character emotions from beat to beat rather than feeling like a pure detective thriller. It's a strong mood piece with a lot of lingering shots and amazing cinematography.
I don't really think people have a problem understanding what the movie is about or what it wants to say. It's not some complex puzzle that needs to be solved. The question is really whether a person is interested in sitting through a long mood piece that's thematic.