Murder At The Gallop was one in a series of Miss Marple/Margaret Rutherford British mysteries...Rutherford certainly appears and acts quite differently from the character of Miss Marple which Agatha Christie created. If you want to see the Christie books presented accurately on screen, view the versions with Joan Hickson as Miss Marple. They work perfectly with the characters, settings and time period of the orginals.
However, authenticity is not one of the reasons for seeing this series of films. Margaret Rutherford is a screen gem...working with her real life husband, Stringer Davis, as co-sleuth (his character never appeared in any of the Christie novels) they form a wonderful partnership. I only wish they had continued this series. 'Gallop' features some excellent supporting actors -- Flora Robson, Finlay Curie and especially Robert Morley. It's filmed in beautiful black and white which captures the early 1960's quite well.
For an entertaining evening of pure delight this is a mystery to cherish!