A Cultural History
I saw this at my school's film club night when I was about 13 I guess, and was blown away by the designs of the suits and the spaceships. Awesome. Pity the story was a bit duff, but you can't have everything.
The plot's built on a foundation of absolute nonsense but above and beyond that basic conceit of a duplicate but opposite earth it still works for me because the performances are so true. Had they have skipped a time line and returned to a slightly different version of earth you could do the same story, I think.