I got the chance to see 2001: A Space Odyssey in the original 70mm Super Panavision a few years ago and yea, it's amazing. Adds so much depth to a film, especially something so visually striking like 2001 or Cleopatra. The 3D movies I have seen don't come close. I think there was also showings of Lawrence of Arabia in 70mm for the 50th anniversary last year but I missed it. 
^
I am seeing Lawrence of Arabia in 70mm next week, I can't wait!
I also caught a special one-night-only screening of Earthquake from 1975. The theatre had hired in technicians to recreate the Sensurround gimmick that was originally developed for the Earthquake screenings back when it was first released. Sensurround basically involves a lot of speakers that pumps out low frequency bass at ridiculous decibel levels - to give the audience the sensation of a "real life earthquake". Or.. of the theatre shaking, I guess. The system was meant to be used in a lot of future releases, but ended up only being used for a handful of films.
A shame, really. It is a much better gimmick than 3D. Certainly made things a lot more suspenseful and urgent during the big earthquake scenes.
This original warning was shown before the film started

ATTENTION!
This motion picture will be shown in the startling new multi-dimension of
SENSURROUND
Please be aware that you will feel as well as see and hear realistic effects such as might be experienced in an actual earthquake. The management assumes no responsibility for the physical or emotional reactions of the individual viewer.Earthquake won an Oscar for best sound design in 1975.
The sensurround didn't actually kick in until quite far into the film. I had almost forgotten about the gimmick when it suddenly hit me like a brick to the face. The build up to the inevitable earthquake is marvelously done too. You watch all the pieces fall into place, and it just hits you; "this is it. It's going to happen now". The sensurround is actually a separate soundtrack, which is basically on or off. It is a pseudo-random noise generator. So that's what you're hit with. A wall of noise and sound waves. It was ... something. I don't really know how to describe it. You certainly feel it in your ears. It feels as if the whole room is shaking. My hair started flailing about randomly. And my eyes watered up. Reading up on sensurround now, I see that the system also caused nosebleeds during original screenings. Good times.
It felt nothing like a real earthquake, but that's a completely different story. I'm really glad I was able to attend this screening, it was
completely sold out!