The Children of Hurin is an assemblage of Tolkien's assorted writings, put together in novel format by son Christopher. The story was begun by JRR Tolkien in 1918, but never assembled as a complete novel. Christopher Tolkien has organized the work into novel format without altering his father's words, save a few grammatical corrections. Thus, this is considered a complete JRR Tolkien narrative.
Darker than Lord of the Rings and more mature than The Hobbit, The Children of Hurin takes place several thousand years before the events of The Hobbit, at a time that the Elves were greater and were strongly allied with the nations of Men. Elves and Men have suffered a disastrous defeat in war, and Turin, the son of the greatest warrior in human history, is trying to reverse their fortunes.
Readers familiar only with The Hobbit and Lord of the Rings might have trouble identifying with the rash Hurin. He has none of the Hobbit-sense of Bilbo Baggins, nor the exceeding nobility and honor of Aragorn. If he is reminiscent of any LotR character, it would perhaps be Boromir, who has the best intentions but does not always see the greater picture.
It has been argued that Tolkien was not so much a writer as the ultimate world-builder, creating a detailed history of Middle Earth, along with languages, literature, folklore and cultures. One cannot read Lord of the Rings without feeling the pressure of tomes of Middle Earth history threatening to burst forth from the pages. There is more story than can ever be told, and The Children of Hurin is an enjoyable chapter in that history. The downside is that the story often reads like a history book. It's not always an engrossing read.
Opinions on this book among Tolkien fans will probably be split into three groups. Avid Tolkien readers will devour this book and beg for more. Readers who liked The Hobbit and Lord of the Rings, but didn't like them enough to read the Silmarillion will find it boring at parts, but worth the read. Fans who love the Peter Jackson movies but are not so in love with the books will hate it.
Overall, The Children of Hurin is a worthwhile read for the average fantasy fan, and a must-read for Tolkien aficionados.