There is no way to encapsulate
2001 into a tidy paragraph, at least not if you enjoy the movie (it remains one of my all-time favorites). It helps to read the book, which is a companion piece to the movie in every sense (they were written concurrently, with mutual feedback). It has some thematic links with
Childhood's End and its transhumanist qualities, as well. That said, they have dramatically different feels; the novel is pretty much straight-up SF, while the movie is, of course, allegorical.
Some spoilers for those who want to read the book:
The movie takes the book farther, IMO, by implying that we not only use tools, but can ultimately become tools without ever knowing it, or perhaps caring. A scene that always chills me is the one where Frank Poole is watching a birthday greeting from his parents; they're bubbly and optimistic, while he looks at the screen as if it were drying paint. In fact, everyone who appears on-screen is more lively than those who don't: Floyd's daughter, the announcers, the interviewer on Earth, even Bowman himself. Though Kubrick himself might deny it, I think it's impossible to deny the idea that he felt technology could--or would--dehumanize people, especially when the only most interesting character in the movie is HAL.
The "Star Child" at the end of the movie is the culmination of everything that came before, a kind of divine state (in the novels, in fact, the aliens are something akin to energy beings), with the preceding events merely a transition, much like life from birth to death (mirrored by Bowman's accelerated aging at the end of the movie).
And so on...
Better stop while I'm ahead.
