I've never read the book in my life, and
2001 is one of my favorite films, even if it confused me at first.
Kubrick is considered a great director because he forces the audience to confront film as something other, and perhaps more, than simply a narrative vehicle. A Kubrick film is a visual experience, more like a photograph or a painting than a novel, and almost any given still frame from 2001 is beautiful enough to frame it and put it on your wall. (It seems important here to note that Kubrick started as a photographer before becoming a filmmaker.) In most of his films, but especially 2001, Kubrick composes these striking images together with just enough of a narrative to form an emotional impression on the audience without making it too overly familiar.
Consider some of the themes of 2001. Do you really think it makes sense to convey those ideas in a way that isn't somewhat opaque? How do you convey the mystery and terror of genuinely mysterious and terrifying themes by turning them into commonplace intellectual concepts and making the audience fully comfortable with them?
2001 conveys more than you can simply put into words. That's why it's a film, not a novel. The novel offers a more literal interpretation of the events depicted, but I think Clarke himself would be the first to tell you they are separate works of art and should be evaluated as such.