Why do so many people think 2001: A Space Odyssey is great?
First of all, one has to accept the idea of deliberate pacing. We live in a world that, for urban dwellers, is incredibly fast-paced. This is reflected in film today with the domination of 'the quick cut' in editing. Now I have no problem with this as an aspect of filmmaking. But it's not the only way to go. There's something to be said for disengaging from the popular velocity. There's something to be said for recalibrating one's patience, one's threshold of boredom. To let a movie demand something of you rather than demanding something of the movie is to embrace the art of film. This embrace takes something associated with popular entertainment and moves it to a higher plane.
2001: A Space Odyssey is film as art. It is visual poetry. And like great poetry it demands something from you. Many people don't care for this. They want escapist entertainment and there's nothing wrong with that. Stanley Kubrick made films for people who wanted more than that. And with 2001 he gave us a lot more with an audacious conceit that is truly staggering in its ambition. He would represent through film the idea of the 'Cosmic Ascension'. Now that takes gravitas.
There is real beauty in 2001, akin to the great masters of painting. The famous 'Space Ballet' is arguably the most beautiful sequence in film history. And it was done without computer graphics. It not only holds up to today's visual standards in a technical sense, it has yet to be surpassed. So much of the story is told visually, something film audiences today aren't used to and many find disconcerting. But again, disconnect from what you are used to, answer to the demands made of you and you may find rich rewards.
The story is epic in its scope. Man was created, by design, by happenstance, in the context of the film this is unknown. Some time after the creation there was an intervention leading to an 'ascension'. Who intervened? God? An alien intelligence? Unclear. Move ahead a million years or so and Man has moved into space using his creation: machines. And here in space will come the great battle. A battle between Man and his creation. Machine will seek to claim the 'Cosmic Ascension' in the place of its creator. Man will triumph over Machine. As they say, "That's deep."