Six Moral Tales is not meant to be a wide-ranging anthology encompassing all moral guidelines, as its title might imply. Instead, they are variations on a theme, best described as stories about a man who has given himself to one woman (either explicitly or mentally) who is tempted by another. All of these men (occasionally through arguably not their own choice) eventually reject these temptations and return to their original object of affection. The similarities between the films do not end there - Rohmer's protagonists certainly share a typical masculine narcissism, though they manifest it in different ways, while his women often attempt to demand their own identities, even as they are being objectified by men who are using them to define themselves. But the movies each present a unique take on these themes, and the feel and intellectual thrust of each is notably and refreshingly original.
Of the six films, I think My Night at Maud's is unquestionably the most impressive. But I think Claire's Knee is also a major work, and La Collectionneuse is very underrated. This is one of Criterion's great boxsets, and hopefully they will be able to produce similar collections of Rohmer's other series in the future - I would at least like to see any of his other films represented! For now, though, this set is a great introduction to his work and one of the great results of France's New Wave.
Links to individual reviews:
The Bakery Girl of Monceau
My Night at Maud's
Love in the Afternoon