I must confess to have never read an Agatha Christie Miss Marple mystery. Since that is the case I have no preconceived notions of what the character should look or sound like. I only know that I thoroughly enjoy Margaret Rutherford in the role. This film was the first of 4 Miss Marple mysteries she made between 1961 and 1965. All were directed by George Pollock who also went on to direct the 1965 Hugh O’Brian version of the Christie novel Ten Little Indians. This Marple film is taken from the novel 4:50 to Paddington and costars American Arthur Kennedy as well as frequent Hammer Films Actor Thorley Walters. The film features a jaunty soundtrack that plays over the credits in this MGM production. Filmed at British Studios in Borhamwood England Rutherford finds herself a passenger on a train who happens to witness a murder on a train passing by through a car window, This sets the plot in motion. A little in joke is her copy of the novel Murder Is Easy by Agatha Christie on her food tray. A nice bit of trivia is that the actor Stringer Davis who plays Mr. Stringer in the film was actually married to Mrs. Rutherford from 1945 till her death in 1972.
From the Rutherford Marple films onward I never tire of watching these old school mystery series be it the Basil Rathbone Sherlock Holmes films to Warner Oland as Charlie Chan and many others. If you haven’t given them a shot then take the time to do so. I think you may like what you find.
Mike's Take On the Movies 
same confession: never read one either, I just find the plots and characters easier to follow when you can watch. Have seen every incarnation of Marple though and I second your recommendation: they’re very addictive. fun facts too, I learn something new everytime I visit!
I haven’t seen any other Marple films other than The Mirror Crack’d with Angela Lansbury. I also really like Peter Ustinov as Poirot in his series of films.