The evolving backdrop of stories about Elves, Men, and the rich tapestry of fictional history is shown here, such as earlier versions of the legendary romance of Beren and Luthien, or the history of the Valar. Not the finished product of "Silmarillion," but older drafts riddled with footnotes and commentary from Tolkien's son Christopher. What's more, it includes linguistic evolution, exquisite poetry, and a time travel story that evolved into something much greater.
It takes a certain amount of geeky dedication to read these books. They are not light reading, and it takes knowledge of the final material to understand their significance. In many of the stories, there is greater detail than is found in the Silmarillion. And in many cases, there are huge differences, such as the mortal Beren originally being an Elf. (Which changes the whole story of Beren and Luthien, and also how we see their distant descendants, Aragorn and Arwen)
Fans of "Lord of the Rings" and "Silmarillion" will undoubtedly enjoy seeing how the unrivalled fantasy stories came to be. Not for newbies, but fascinating for major fans and anyone who likes seeing how Tolkien's writing evolved.