I had the same reaction many people in this thread had to it my first time. My relationship with 2001 is the most bizarre I've ever had with a film. I first tried watching it early on in my movie loving life. I couldn't make it an hour in and turned it off, dismissing it as overrated poo. "A classic? One of the best films of all time!? HA! YA RIGHT!"
A year or so later I was more informed on the history and theory of the film and tried it again and got through it that time. I still didn't like it and struggled through it but I felt accomplished I at least got through it and had put another classic film under my belt.
After that viewing I would think about it from time to time. It would come up in forum conversations, I would hear filmmakers talk about how influential it is and all that and I would think "What is it about this film?" I was stubbornly against the film for being nothing but a well shot bore. I forcibly rejected its intent and tone and just said "I hate it because it doesn't go anywhere and that's it. There is nothing to get." I would arrogantly put it on "my most overrated films ever" list and smile with a smug satisfaction of defying the popular consensus. Ya, I went through a bit of a movie snob, contrarian phase that was blessedly short.
One day I got a bug up my butt to watch the film again after being taken by a well written piece on a forum from a fan of the film. All of a sudden I felt like I just had to see the film again. I went to the store and got it on Blu. This is going to sound pretentious and made up but I swear it's true. As I sat there watching it again, I just sort of...got it. I was loving it. I was swept up in the visuals and the sound and I was enjoying coming up with my own theories on the film. 2001 is not a movie you can just passively watch once. It really is an experience that demands your attention. You can't just be in the mood to sit and catch a flick and come away satisfied. You have to want to really experience a film. Again, I sound pretentious but I really don't mean to, it's just how I feel.

I totally understand why some would dismiss the film and not even finish it. It defies all of the story telling standards we are used to from 99% of the films we watch. Even the more enigmatic films we may watch and enjoy have more of a standard structure than 2001. There very little dialogue and what dialogue there is doesn't do much to further the plot of help us understand what is going on. There is no protagonist until the film is reaching it's end, no character arc of development, the story is all told in visuals and interpretation and is not made clear once throughout the run time. It's just not like most films.
I think 2001 was startlingly ahead of it's time. I'm shocked it was allowed to be made the way it was. I think every film buff owes it to themselves to watch it once all the way through and leave preconceived notions at the door and just it let it
happen to you. I think anyone can at least appreciate the visual marvel that it is, if nothing else.