2001: A Space Odyssey is the sort of movie that frequently gets called "difficult". Which is, ultimately, never true of a film that costs that much money laid out by a major studio (MGM, in this case), though I'll concede that if by "difficult" one means "the ending is a deliberately obscurantist explosion of borderline nonsense", then I can see why you'd think that.

Here's my notion: 2001, it is generally known, came about because Stanley Kubrick, fresh off the triumph of Dr. Strangelove, wanted to do hugely ambitious things. And it was in that capacity that he reached out to Arthur C. Clarke, the great science-fiction author who was the most concept-driven and technology-oriented of the big names in genre fiction of the mid-'60s, and suggested that they make "the proverbial 'really good' science-fiction film". Through a great deal of wrangling that needn't bother us here, Clarke and Kubrick ended up collaborating on a pair of virtually identical narratives, both released to the public in 1968: one of these was the screenplay to 2001: A Space Odyssey, the filmed version of which premiered in April, and the other was the novel 2001: A Space Odyssey, which was published months later, so as to avoid stepping on the movie's toes.

There are many tiny details, and a couple of substantive ones, where the book and the film split, but the biggest one is more a matter of tone and focus: Clarke's novel is, generally speaking, explicit about what's going on, and Kubrick's film is, generally speaking, cryptic. I think this is no accident, and not a flaw with either version of the story; it strikes me and has always done so, that the book and the film are complementary to each other. Both of them address roughly the same themes using the tools which their respective media are best at: the book is about the communication of ideas in a clear way, while the movie is about the relating of moments and sensations in a series of fluid images. The one is concrete, the other is intuitive. The one is descriptive, the other is experiential.

Shorter: if you don't understand what the plot of 2001 contains, and it really matters to you, read the book. That's what it's there for.

Anyway, this is begging the question, a little bit. To be frank about it, I think that getting too tangled up in the "why" and "what" in 2001 is missing the point of the whole thing, which is that the film specifically intends not to clarify things - it is a story about events beyond human conception, very literally. The final 30 minutes of the film depict a process that we, are homo sapiens are insufficiently evolved to comprehend; the greater sin would be if the film did make any sense in this passage. In seeing what happens, and not knowing what it means, we're occupying the exact same place as the human protagonist, until such time as he ceases to be the "human" protagonist.

That's the ending, anyway. At almost two and a half hours long, 2001 is about much more than its visually transporting, narratively obtuse conclusion. It's part mystery, part "what if?" ethnography of a speculative future (that was, in virtually every regard, wildly optimistic about what life in the year 2001 would look like; though in retrospect, the most shocking thing is that the film would predict video chatting and self-aware computers, but not touch-screen control of either of those things), capped with a depiction of spiritual development that would seem altogether New Agey if the film weren't so rigidly materialistic in every single detail. Most of all, it's a good old-fashioned space adventure as warped into new forms by an author noted for his fixation on scientific plausibility and a director whose approach to genre had consistently been to subvert norms; the most significant element of 2001 is, in fact, that it's an early example - among the earliest in the English language - of an anti-genre film, in this case an anti-thriller. Take the details of the plot (hidden objects on the moon, insane killer computers, aliens), and give it to just about anybody, and you get a snazzy little blunderbuss of intense moments, probably clocking in at about 70 or 80 minutes. But in Kubrick and Clarke's hands, these materials are grist for one of the most purposefully boring movies ever made on American studio dollars.

Which sounds like a criticism, but I mean it to be the highest praise. Thematically, 2001 has one overriding interest that it examines from multiple, wildly different angles: the human's interest in interacting with the world around it by means of technology. We are the tool-using animals; we are the animals that manipulate reality using labor-saving devices. And with that as its primary focus, the film spends an utterly, wonderfully absurd amount of time watching people utilising future technology. There might not be any other hard sci-fi film in history where the lingering over future tech feels so focused and keenly tied into the theme as this: the languid, almost endless shots of people manipulating buttons to make spaceships go, or watching people walking in zero gravity environments, or studying the rules of weightless toilets, or eating food in space; all of these individual moments build up to one statement, which is "this is how technology will enable us to live". No film to boast such groundbreaking, still magnificent visual effects work - and 2001 is probably the single greatest triumph of visual effects in the 44-year window between King Kong and Star Wars - has ever done it with so little interest in providing spectacular entertainment. Quite the contrary: the immensely convincing effects work (which, according to the credits, was all designed by Kubrick himself, though it is known that he somewhat bullied his way into that credit, which rightfully should have been more fully shared with several other men, among them future VFX icon Douglas Trumbull), eye-popping in itself and still fully convincing on even the sharpest 70mm print or in the bright crispness of Blu-ray (and I have seen the movie on both formats), the superbly involving and immersive effects work, is all presented in the most confoundingly banal way.

A film about humankind and technology; but not a terribly optimistic one, you see. There is the way that the first tool ever used by a proto-human is seen in the film as having been a weapon; there is the legendary cut from a falling bone to a drifting orbital nuke, bluntly suggesting that after millions of years we're still using all our cunning in the most savage, animal ways; there is the fact that such drama as the film actually possesses hinges on an artificial intelligence created so perfectly that it can have nervous breakdowns and go on murderous rampages, at which point the only thing left is to kill it - killing it being, in 2001, the one thing we're really good at. At any rate, the film's major thesis about the marvels of interstellar travel is that it's depersonalising and tedious, and the way that people live in its fantastical vision of the year 2001 is full of the same bullshit and nonsense as life in 1968, or every other year in the history of civilization. It's such a well-worn argument that I'm embarrassed to even bring it up, that the only character in the movie that has real feelings and whose fate is genuinely affecting is the mad computer HAL-9000 (voiced in the incomparably bland and soothing tones of Douglas Rain), while the actual people - including the ones that HAL kills - are dull ciphers. The astronauts Frank Poole (Gary Lockwood) and Dave Bowman (Keir Dullea) - the latter is our nominal hero and the focus of all future human evolution, which is undoubtedly why Kubrick and Clark gave him a surname referencing weaponry - are for all intents and purposes indistinguishable, and completely untouchable by emotions; Frank's birthday message from his awkward parents elicits barely any kind of response from him at all. The first human lead we meet, Dr. Heywood Floyd (William Sylvester), says virtually nothing that's not mindless small talk, even when he's presumably briefing a team with information that can hardly be all that revelatory to them, mostly coming off as bureaucratese. It is the first film where Kubrick played a game that he'd return to frequently in his career: cast lifeless actors and use their very lack of affect or personality to comment on the character they're playing. Sylvester appeared in the 1964 horror film Devil Doll, which put in an appearance on Mystery Science Theater 3000; there, one of the snarking robots observed during a particularly leaden moment of vacant staring, "This is the scene where Kubrick said, 'That's my Heywood Floyd!'", and even as a joke, that has a tang of truth to it.

Now, all that being said, the film is still magnificently watchable. Depicting tedium does not have to be itself tedious, and the actual effect of the movie is both mesmerising and invigorating, I have found; Kubrick, his cinematographers Geoffrey Unsworth and John Alcott (the latter receiving only an "additional photography" credit, in his first of four collaborations with Kubrick - the only cinematographer to come back for more of the director's micromanaging after the first time), and his editor Ray Lovejoy collaborated to make one of the small handful of movies that fully and legitimately deserves to be called visionary; and that's without mentioning the music, which is a foolish thing not to do. 2001 was the first film of the director's career where the music choices were consistently thoughtful and extraordinarily important, especially his use of three pieces by GyΓΆrgy Ligeti (without Ligeti's permission), with the composer's jarring micropolyphony creating a sense of unearthly aural sensation, chaotic without actually being formless, that ideally suits the film's depiction of human beings getting in out of their element (of course, the iconic use of the fanfare from Richard Strauss's "Also Sprach Zarathustra" - itself based on a Nietszche work where he discusses, among other topics, the idea of the Superman, which makes it thematically cunning and aurally pleasing - is also brilliant, though a bit damaged by almost a half-century of parodies). I can only complain about the pairing of the first space travel sequences with Johann Strauss's waltz "By the Beautiful Blue Danube", which though it creates an exquisite marriage of image and music, also serves to make the sequences that are, presumably, meant to especially showcase the tooth-grinding dullness of space travel, instead come across as especially poetic and lovely.

But anyway, the images, the editing; 2001 is an impeccably well-crafted piece of cinema. Visually, it is anchored by a handful of repeated shots and images that echo each other (the alignment of celestial bodies and the film's famed black monoliths; the repetition of set-ups within the spaceship Discovery that especially stresses the limited scope of the ship and life within it), giving it a consistent visual shape - it is a movie deeply in love with circles, for reasons that are obviously linked to its theme (cycles, repetition, species replacing species only to be replaced by other species). The stillness of its images and the length of its shots gives it a hypnotic, insinuating sense that is occasionally pierced by quick or dramatic cuts at certain moments - the interpolation of "Also Sprach Zarathustra" with the image of an ape-man wielding a bone and non-diegetic shots of a tapir dying is not the film's most famous sequence, but one that I particularly admire for its quick transposition of triumph, awe, and cruelty. Later, HAL's murders are committed through piercing beeps on the soundtrack and the brutal cuts between the sterile white sets of the spaceship interior (the three production designers do excellent work throughout of making a future that looks both plausible and lifeless) and blaring right lights. Editing is not only used to indicate violence in the film, though it does an outstanding job of doing so.

All together, this is extraordinary filmmaking, creating intellectual arguments mostly through image and music, with its story shoring up its form, rather than the other way around, as is typical of mainstream filmmaking. The only thing that the film can be knocked for is that the sheer scale of its themes makes it an easy target for accusations of being kitschy, or pretentious, or overly pop-sciencey; all of which are criticisms I've heard leveled against it, and they all strike me as coming from the same place. Most art doesn't deal with the actual big questions - What, if anything, is the nature of God? What is moral behavior? What is it to be "civilized"? Where does humanity fit into the rest of the universe? - and there are plenty of people who get very irritated when it tries to, for reasons that I'll not pretend to understand, or care about. At any rate, that 2001 asks questions in these areas is, I think, an absolutely noble trait; that it asks them in such a well-formed, bold mix of experimental and mainstream filmmaking technique, with such one-of-a-kind images and structural conceits, is why it's a brilliant achievement of cinematic art. To me, it's enough to make it Stanley Kubrick's masterpiece, and one of the greatest films ever made.