ddickinson: The sad thing about Tolkien's works is that he had so much written that never got finished or even published. His son is slowly releasing some of it, but sadly we will never see the whole story, due to the epic size of the world Tolkien created.
Yeah, it's a shame we'll probably never see everything he had envisioned.
But while we're on the subject, why do you think he wrote LoTR? (and all the rest of the mythology)
Tolkien considered languages inseparable from the mythology associated with them, and he consequently took a dim view of auxiliary languages: in 1930 a congress of Esperantists were told as much by him, in his lecture A Secret Vice, "Your language construction will breed a mythology", but by 1956 he had concluded that "Volapük, Esperanto, Ido, Novial, are dead, far deader than ancient unused languages, because their authors never invented any Esperanto legends"
For me this quote, and the fact that his area of study and passion was languages, suggests that he may have created the whole mythology around the languages, as a means of having the languages survive.
I don't know if that's true, but I've always liked to think it might be, and that it makes the effort he invested all the more spectacular...