Completely Spectacular
This film really does have to be seen in 70mm to fully appreciate the detail and the intended feel. It's a visually mesmerizing ride, and a small screen just won't do it full justice. You need to see it on a big screen to appreciate the violent ecstasy of the ape-man's discovery of tools, the vastness and disorienting directionlessness of space, and, of course, the "beyond the infinite" sequence.
The sound design is amazing, too, particularly the breathing in the spacesuit, the quiet of space (one of the few films to get that right), and the unnerving beeps and blares of alarms.
In some ways it is dated (Pan Am?), but it still fares better than anything else made during that time period. Most importantly, it holds up as a magnificent piece of art, thought-provoking whether you like it or not.