Dunno, I've only seen Barry Lyndon once and i really enjoyed it without having to see it again. But Clockwork Orange i couldn't get into at all 
I agree with you about Clockwork Orange. I can see why it was controversial at the time but it now looks horribly dated.
A Clockwork Orange is great, though the older I get, the less I enjoy it.
I've actually got to jump in here and mention that 'A Clockwork Orange' is my favorite movie. I don't find it dated and I can pretty much enjoy it any time I watch it.
As far as 2001 goes, I'm not on board. I get it, but it's not worthy of another 2 hours of my life. When this came out over 40 years ago, we didn't have personal home movie players. People couldn't pause, rewind, etc. When you went to a movie you immersed yourself in it. That, I think, is what helped this movie. Also, the space programs and science fiction were at the forefront of Americana. I remember seeing Alien in the theater and being blown away! And, by 'blown away', I mean scared sh*+less.

I'm not one to watch too many movies twice, but in the interest of sharing, here are a few of my favorites that have been watched much more than once by me:
A Clockwork Orange
Love And A .45
Leon The Professional
Romper Stomper
Buffalo 66
Man Bites Dog
Spanking The Monkey
Reservoir Dogs
Stand By Me
Across The Universe
Sin City
Lucky Number Slevin