Rather dry reading. Interesting material, but definitely more encyclopedic than narrative. Devotees of Tolkein's world will enjoy this book.
I suggest approaching this book as if you were tackling a research project and not a novel.
Challenging but rewarding if you persevere.
I call this book The Bible of the Middle Earth, and rightfully so. It provides a lot information and background prior to the events of The Lord of the Rings and the Hobbit. Of how things were created, of the coming of the Elves, of the wars, Sauron's beginning, etc. it just fills up the things that were not explained before and the things that left you wondering or wanting to know more about. You definetly need to read this book if you're a Tolkien fan.
Biblical in it's language and style. If you want the history of Middle Earth, the first through third ages, this is for you.
Prequel to the "Lord of the Rings" and the "Hobbit", much more Old Testament-ish than the hobbit books.