Science Fiction
R.U.R. is science fiction—though back in 1920, science-fiction wasn't exactly the genre it is now. H.G. Wells had already written The Time Machine and other sci-fi works, but there wasn't any Star Trek or Star Wars or a lot of the novels and works we associate with that genre now. That meant that Čapek's readers (or playgoers) weren't familiar with sci-fi the way you would be. They didn't know what robots were, as the most obvious example. Genres (like robots) take a while to build up and understand.
So, a lot of the play is given over to talking about science-fiction concepts that you are probably already familiar with. What is a robot anyway? How does it work? What is it good for? You already know some, or many, of the answers to that, but Čapek didn't—he had to think about it. And that, in turn, can maybe make you question what you think you know, or know you think, about robots as well.