This series was superb in every way and is one of the finest things the BBC ever produced. It could never be done today - there are just not enough authentic actors and impossible to find such unspoiled locations. The cast in every episode are so quintessentially English (excepting, of course, the odd Scot, American and so on) and they sound exactly right for the period. The music is wonderful, the costumes, cars, interiors - everything is perfect.
My only severe criticism is that the BBC have never bothered to try to restore these, or they used inferior materials to film them in the first place - whatever the reason, the picture quality is pretty awful and the sound not great, which is such a pity. These productions are unique treasures and deserve the best attention to make the picture and sound live up to brilliance of all the rest. Let's hope someone will make the effort to save them, as was done when the blu-ray of the BBC Pride and Prejudice was released. Such a huge improvement on their old DVD release.
I still have to give the set five stars as in every other way this Miss Marple is a masterpiece.