The film does not have a traditionally strong script. It's a primarily visual and emotional film that was the product of a singular vision that, to put it bluntly, didn't require such a crutch. The performances are not heart-wrenchingly emotional: such dramatics would have betrayed the entire essence of the film. This is a movie about the mechanisation and sterilisation of the human being in the face of technology. The fact that Hal, the ship’s on-board computer, delivers the most moving performance isn't coincidence. In fact, the entire point of his character was to demonstrate how machine was replacing humanity and how we are becoming parasites feeding off a host of our own creation.
Many have (unfairly) criticised the film for being too slow. In reality, the methodical pace in 2001 was entirely intentional and reflected the "message" exactly as Kubrick wanted it. It was not a pointless dilution. At the beginning of the film we see man in the routine of natural life. Things move slowly as the missing links go through their natural life, engaging in mechanical behaviour. Then, they encounter the monolith, they suddenly experience thousands of years of evolution and at once and the action picks up to a ferocious battle between the now technologically enlightened tribe and one which was left in the dark. When we cut to the year 2001, we see the same thing. Man has evolved into technological mastery, but he is in stagnation. His machines dance amidst the stars in methodical routine. The colleagues aboard the initial space station speak to each other in polite, sterile "technical" terminology. Man is once more going through his existence in a mechanical depression. Then Dave encounters the monolith again. There is no quick-cut that cuts all but what serves the plot. The explanatory sequences serve the style of film that Kubrick was trying to create. Not narrative adventure in the traditional sense, but a documentary-like examination of the state of man on the verge of his rebirth.
2001 makes a philosophical statement about man's place in the universe, using images where other films use words. It was not intended to be viewed as entertainment, to be forgotten about, rather as a piece of art to be contemplated, and it succeeds magnificently.