"The Fall of Arthur" is a lengthy (954 lines), alliterative, and unfinished work. Tolkien loved reading the Arthurian myths as a boy and in the early 1930s began to write "The Fall," but ultimately abandoned it, though various outlines and drafts survive in addition to the final unfinished text (source: The J.R.R. Tolkien Companion and Guide, Christina Scull and Wayne Hammond, p. 56). Ultimately Tolkien fell away from the Arthurian stories, which he regarded as too mixed with other elements and influences and lacking enough of Britain's character; the stories were "associated with the soil of Britain but not with English," according to Tolkien. Hence his reason for writing The Lord of the Rings and its supporting legendarium as told in The Silmarillion and elsewhere, which serve as an alternative mythic history of England.
Like "The Legend of Sigurd and Gudrun" I fully expect that this will come and go without huge fanfare or sales. But for hardcore fans of Tolkien and Tolkien scholars, it's huge. Maybe not quite as huge as say, the discovery of Excalibur, or Arthur returning over the sea from Avalon to set our darkening world aright again, but huge nonetheless. And it just might prove to be a cracking good read; again quoting from Scull and Hammond:
Humphrey Carpenter comments in Biography that in his work 'Tolkien did not touch on the Grail but began an individual rendering of the Morte d'Arthur, in which the king and Gawain go to war in "Saxon lands" but are summoned home by news of Mordred's treachery .... It is one of the few pieces of writing in which Tolkien deals explicitly with sexual passion, describing Mordred's unsated lust for Guinever (which is how Tolkien chooses to spell her name .... ' But here Guinever 'is not the tragic heroine beloved by most Arthurian writers'; rather, she is a 'lady ruthless / fair as fay-woman and fell-minded, / in the world walking for the woe of men.'
Hat tip to the Mythsoc listserv for the news.