The problem with reviewing or even understanding 2001, today, is that you are critiquing it out of time.
1st, that it was "all special effects," well, yes, but more importantly they are "accurate" special effects. Even today, 2001 portrays the PHYSICS of space travel better than any other movie ever made. It is one thing to use computers to create "action" with special effects, 2001 portrayed "space." I can't emphasize this enough. In 1969, this was simply revolutionary. Star Trek was fantasy, we had men going to the moon and trek was clearly scifi. 2001, at the time, seemed real and possible. It was science fiction in the classic sense that the science was real and the story was fiction.
It must be hard for people 40 years old and younger to imagine this period in time. About 12 years 10 years prior, the world changed with Sputnik. We were moving from weather balloons to weather satellites, science was changing everything and we were dreadfully afraid of the Russians beating us. 2001 was a view of space travel attainable from the perspective of the Apollo missions. It was astutely political. It asserted evolution. It worked in "our" albeit future, world.
Unfortunately, 2001 also suffered from concepts that are difficult to visualize. I agree with another post, it is almost impossible to understand without having read the book first.
Still one of my "Most Important Movies Ever Made"