This is a really, really good musical. This would be a really, really good film if there were no songs in it, and the songs are terrific. From the funny "Protogorically correct" and "What a comforting thing to know", to the heartbreaking "Once I was loved" or the romantic "He danced with me", they are all beautifully tuneful and add to the portrayal of the characters. The choreography, settings and costumes are just lovely (it was largely fimed on location in Europe).
The plot and characters, however, are the best things about this film. Plot? Yes, this is Cinderella. However, it is utterly vital that the Prince marries a foreign princess who will bring an alliance to support his small country, not some penniless girl from the nearest castle.
The characters really spring off the screen (the actors are excellent- Edith Evans, Richard Chamberlain, Kenneth More, Annette Crosbie, etc)- from the King, worried and overcome by events, to the overworked and acerbic fairy godmother, the wonderfully nasty stepmother and her two silly and spiteful daughters, the Chamberlain, and of course Cinderella and the Prince themselves, who are actually interesting and not just "the heroine" and "the hero", they are all a joy to spend time with.
I've been showing my video of this to people for years and even the most cynical have always liked it. It's just good. Buy it, watch it, fall in love.