One of the stories in the Silmarillion is the Tale of the Children of Hurin, or the Tale of Turin. A personal tragedy, set against a bleak background. it derives many elements from the Kullervo tale. The chapter in the Silmarillion dealing with it was brief, but poignant. Fragments of a longer actual proper narrative version appeared in Unfinished Tales and other works.
I always though it would make a great story split out on its own. But since Christopher Tolkien had apparently sworn off writing new stuff to cover the gaps, this seemed another tragedy: glimpses of a work that could never exist (Tolkien himself covered this theme in Lead by Niggle). Now we learn he has been secretly working on this for quite a while. I am looking forward, albiet trediply, to reading the complete lay of the Children of Hurin. I hope he did it proud.