2001 is a film quite unlike any other to date. It's difficult to put in a box - you could call is sci-fi, but it breaks many sci-fi conventions. It breaks many conventions of any genre - for the first time, Kubrick was a law unto himself.
My take on the whole "mystery" aspect of the film is that it's meant as an *experience*, more than a fictional narrative. This isn't a movie about good vs. evil or the perils of technology (although it contains these elements). This is a film that causes the viewer to experience a feeling of wonder, awe and yearning.
Kubrick made a comment about it being a "religious" movie. In many ways it is.
From the time it was released some people have called it boring or emotionally detached, but I dissagree. Over time the film has acquired a status of "legendary", and has penetrated pop culture in ways no other work has done. In spite of it being a subjective experience, it's had a profound effect on those who have seen it.
Far from being unemotional, I found the closing scene of 2001 to be the most touching expression of human optimism ever put to celuloid.
Sci-fi geek: 2001 sucks man, where are the exploding spaceships and wierd looking aliens?
Me: Wow.. I'm so past all the crap I watched as a kid. 2001 rules!