It's definitely a lot slower paced than our current ADD society is used to. An esteemed director like Kubrick's movies would seem unbearably slow to many.
I have never made it all the way through one without falling asleep. 2001, Blade Runner, Dr. Strangelove.... Even movies loosely associated with Kubrick like A.I. cause me to nod off. I have to stop when I'm nodding off and come back later fresh in order to finish.
Maybe it would be different if I had seen them in theaters.
Gladiator was also amazing!
There's still chances to see 2001 in cinemas! It gets re-released somewhat regularly for anniversaries and Kubrick retrospectives, etc. I was born long after 2001 came out, but I've seen it on cinema screens many times. It was so far ahead of it's time and looks so incredibly good in 70mm that it's mind boggling to consider that it was actually made in the 1960s!