Stunning cinematography and groundbreaking visuals, introducing numerous things that haven't been done in cinema before, all without computer graphics. Stunning and way beyond its time
Epic soundtrack and enigmatic atmosphere
Most accurate, scientific portrayal of Space
Immense scale and scope of the film, exploring "big ideas" like a man's place in the Universe, technological progress, (artificial) intelligence, man vs. machine, etc; and narrating the entire history of humanity and evolution of the humankind
Story being conveyed mostly through visuals, symbols and musical cues rather than dialog, intentionally leaving many of the ideas and scenes open for interpretation. It's challenging
I personally love it, and I'm not even much of an arthouse film fan in general... However, I understand why many find it boring, too-long, pretentious, etc. It's very polarizing, kind of a love it or hate it kind of film...
I also read Arthur Clarke before I watched the movie, both the novel of the same name which he wrote while working on the filmset with Kubrick, and his previous works that influenced the creation of the movie, so maybe I just had more reference points for the story... If you want more story and more explanations, it's worth taking a look at the "sequel" which was not directed by Kubrick, so it's a very different style and also more accessible: 2010: The Year We Make Contact