I saw this film several times on TV as a kid in the 60's. I enjoyed in thoroughly. Jim Backus's hamming is delightful. The music was borrowed wholly from Peer Gynt by Grieg -- from Morning Mood to Hall of the Mountain King.
Another reviewer comments on the colors (in a rather unsympathetic and grinch-like manner ). You must remember -- THERE WERE NO COLOR TVs IN 1957! Anyone with any knowledge of media knows that! They only existed in factories and a few individuals. They did not hit the market until 1958, and they were not in major use until after 1962 - at least among the people in my neighborhood. Anyway, the colors used had to make appealing greys when viewed in black & white. Hence, you will get some pretty odd colors. The use of such garish colors probably contributed to the development of Op-Art and Psychedelic art in the 60's. However, I digress, anyone who lets technical details get in the way of enjoying a child-like bit of fluff, especially one made on a small budget for TV, should stay up on his mountain, and never be let into who-ville.
Also, the pace of the film has been criticized. Well, the pace editing in films has sped up in the last few decades (look at Ridley Scott's work --- sheesh, you need seatbelts in the theatre!) You must let yourself go with the flow and the speed of the film. Let yourself be taken by the music and the performances. Basically, if you liked Brigadoon, then you should like this.
My recommendation -- if you are a child at heart, and want a delightful heartwarming film, filled with great music, seeing great performers enjoying themselves, then watch this film. Otherwise, go rent "The Sorrow and The Pity".