Like many, I imagine, I stumbled on Evangeline Walton's four-part adaptation of the Welsh national epic, the Mabinogion, when it came out in paperback in the 1970s. It was immediately obvious that these books were something special, a level above some of the derivative Authurian "fiction" that even then was flooding the market. Not being an antiquities scholar or linguist, I have nothing to say about how authentic the author was to the original piece.
I am excited to see that the "quartet" is being re-issued and I can buy it for my son...not sure if I can dig the paperbacks out of the basement. They did have excellent cover art.
The author emphasizes the magical elements of the myths, and the emotional reactions of the characters, placing them in a half-real sort of dream-time. The language is sparse and understated, however, counterbalancing the less-than-believable events, and lending a patina of antiquity. As I recall, however, there is a (pseudo)-psychoanalytic slant to things, lending a decidedly 20th-century slant. The stories are old, but re-told for today. Not too much sex or graphic violence either...perfect for the teenager ready for something a bit deeper and modern in outlook than The Once and Future King, more complex than Lloyd Alexander's quintet (Black Cauldron, etc.) by a quite a bit (these books are probably inappropriate for pre-teens), but not quite as cutely "radical" as Mists of Avalon.
Maybe its just nostalgia for how great they seemed when I was a lot younger, but I thought they were great and intend to order the re-issue.
New Fifth printing Del Rey