May I add a foreigner's point of view to the ongoing discussion?
> >> Have you noticed that the literarily prestigious examples of this, at
> >> least
> >> in English literature, all date from before the mid-17th century?
> > I'm not sure how that affects the aesthetic question. In any case there
> > are many many excellent modern movie/TV series/operas/plays that closely
> > follow modern sources
> Those are open adaptations to the dramatic medium. Not retellings in the
> medieval/Renaissance sense. (So, for that matter, is most of Shakespeare.)
> The point in a general sense is that, since the mid-17th century,
> originality has been prized in literature, and to find evidence that it is
> not prized, you need to go back to an earlier era that took a very different
> view, that all the stories had been told, essentially, and that all writers
> could do was retell them.
This reminds me of the French "Querelle des Anciens et des Modernes", at the end of the 17th century (start: 1687; end: 1694). I believe it had quite an impact on European literature at the time, and can indeed be seen as a turning point when originality became prized for its own sake.
> > There are even cases where the source and the copy are within the same
> > form: e.g. The Threepenny Opera follows the Beggars' Opera (admittedly not
> > in English literature, but not sure why that distinction would matter.)
> Not really prized for literary prestigiousness, but for the music (which is
> entirely original). And I specified English literature because I'm not
> entirely certain how far my rule applies outside of it.
> > There are several cases of modern novels and poems that follow older
> > sources fairly closely e.g.
> > The Once and Future King, T.H. White (follows Mallory quite closely in
> > long sections)
> Not really. Quite a reinvention - and of a traditional story that long
> predates Malory. Expansions into novel form of something told in a more
> condensed earlier form are not really the same thing.
In French literature, one could name tons of examples of famous works of art of the 19th and 20th centuries extensively quoting or retelling ancient stories. Victor Hugo's _La Légende des Siècles_ (1859, 1877, 1883); Jean Giraudoux's _La Guerre de Troie n'aura pas lieu_ (1935), _Électre_ (1937); Jean Anouilh's _Eurydice_ (1942), _Antigone_ (1944), _Roméo et Jeannette_ (1946): these are just a few examples that spring to mind.
However, as you point out, most if not all of them are really reinventions of these stories, developing the characters very differently from the originals, even if the events closely follow the original story.