Metropolis is widely held to be the beginning of modern science-fiction film. Its imagery is certainly iconic; the famous robot was the basis for the design of George Lucas' C-3P0.
But until recently, it was always known that the original version of the film, which had been heavily edited to make it palatable to distributors, was forever lost.
Most fortunately, a nearly-complete version of the original was found in 2008 in a museum in Argentina, with an extra 25 minutes (approximately 20% more footage). The whole was restored, and was debuted in its newly-restored state a month or so ago in Berlin. For aficionados of the genre, this was akin to finding the missing 2 commandments. Nearly a whole half-hour of additional film, which not only fleshes out the characters and plot, but adds entirely new sub-plots and a ton of extra detail. (Including the original 1927 score.)
It's getting a very limited US release; you can see it if you live in New York, Los Angeles, and Cleveland (!). It will be released by Kino.com sometime this year, but in the meantime, you can feast your eyes on the trailer they have put together. I can't wait to get this sucker in my collection.