What makes a great fantasy movie? Why are some fantasy movies classics and stand the test of time while others bomb and are forgotten? I believe the best fantasy movies are the ones rooted in real history, real mystery religions, real symbols. The realness resonates within us. Two of the classics, IMO, are The Dark Crystal and Conan the Barbarian. I would have gotten into The Lord of the Rings, but that's way too much to handle.
Jim Henson, with his flowery shirts and psychedelic experimental films, had to most definitely have been a product of the '60's and the counterculture movement. I'm not sure of what his specific religious beliefs were, if he was into New Age whatever that means who knows. He did make various short films that expressed his counterculture-like interests, including Youth 68 and many psychedelic animations as seen in Sesame Street. For The Dark Crystal, working with Brian Froud, they researched ancient religions and world history and created this fantastic yet familiar world. And "familiar" is key. Other fantasy films probably haven't worked as well because they haven't based designs and story on the research of real human history, 
art, and folklore. This should be noted if you're a production designer or art director. See the pics for more info, and see The History Channel's Ancient Aliens series. And also, because the film really doesn't have much dialog (in fact it was originally meant to have a made-up language with subtitles), the images are that much more important in telling us what this world is about, and it's that much more immediate when the images are familiar.
I think there seems to be a counterculture movement whenever there is a disillusionment with society, where the world is in chaos, and people seek answers "elsewhere," and this movement reappears throughout history. More or less around the Civil War, theosophy arose, and possibly inspired the Romantics, Pre-Raphaelites, gothic literature, Art Noveau, etc. These artforms referenced ancient civilizations and mystical occultism. Around WW1&2, arose Art Deco (lot of Mayan and Egyptian motifs), Nazi's occult usage, L. Frank Baum, JRR Tolkien, and Conan's author, Robert E. Howard. They all take from ancient esoteric history. Around the Vietnam War arose the so-called New Age (ancient and especially eastern mystical stuff) and I'm guessing George Lucas and Jim Henson might have been influenced by that. I don't care much for labels such as New Age and Theosophy, plus I haven't looked much into what those are defined as exactly, but I like to research and reference historical cultures and ancient ruins, and I find significance in those things. There seems to be more studies nowadays exposing this pre-history of man, like of Mesopotamia or before. A pagan world before the Judeo-Christian-Islam organized-religions-coopting-for-political-purposes mess. Ancient cultures around the world built henges of heavy stone and monuments to track astrological movements and planetary alignments. It would be foolish to call them primitive. Key figures to check out include Michael Cremo, David Hatcher Childress, and Graham Hancock. My point being, these movements towards rediscovering ancient history and knowledge, seems to be in response, a counterculture, to a disillusionment with western, mainstream, status quo thinking.
John Milius, director of Conan the Barbarian, is buddies with George Lucas I'm sure from the American Zoetrope days. I'm sure he's picked up that Joseph Campbell influence. Campbell had once stayed at Nicolas Roerich's Master building, which has a library of ancient texts, eastern religious books, etc. Mystic Roerich was a influential in getting the eye and pyramid on the back of the US one-dollar bill.In the Conan the Barbarian dvd commentary track,
Milius said he wanted the movie to feel very real, as if based on an ancient prehistory of man. Robert E. Howard created an age called the Hyborian Age, which was almost post-Lemurian, post-Atlantean. There's a scene where Conan gets his sword from a skeleton, a 8-feet tall ancient Atlantean ruler. Scholar's like Joseph P. Farrell talks about how the greeks, hopi, mayans, iroquois, aztecs, and the bible all talk about an ancient war with a giant elite race. The doc Mysterious Origins of Man narrated by Charlton Heston is also interesting.
