Consider this -- J.R.R. Tolkien's fantastical epic "Lord of the Rings" is only the tail end of his invented history.
Yes, Tolkien spent most of his adult life crafting the elaborate, rich world of Middle-Earth, and coming up with a fictional history that spanned millennia. And "The Silmarillion" was the culmination of that work -- a Biblesque epic of fantasy history, stretching from the creation of the universe to the final bittersweet departure of the Elves from Middle-Earth.
A complete summary is impossible, because the book spans millennia and has one earth-shattering event after another. But it includes:
*The creation of Tolkien's invented pantheons of angelic beings under Eru Iluvatar, also known as God.
*How they sang the world into being, and the creation of Elves, Men, and Dwarves (hobbits are not really covered).
*The legendary love story of Beren and Luthien, a mortal Man and an Elf maiden who gives up her immortality for the man she loves.
*The attempts of the demonic Morgoth and his servant Sauron (remember him?) to corrupt the world.
*Feanor and his sons, and the terrible oath that led to Elves slaying one another.
*The Silmarils, the glorious gems made from the the essence of the Two Trees that generated the world's light.
*Elves of just about any kind -- bad, mad, dangerous, good, sweet, brave, and so forth.
*The creation of the many Rings of Power -- and the One Ring of Sauron.
*And finally, the quest of the Ringbearer, Frodo Baggins, and the final battle that would decide the fate of Middle-Earth.
If you ever were confused by a reference or name mentioned in "The Hobbit" or "Lord of the Rings," then chances are that "The Silmarillion" can enlighten you about what it meant. What is Numenor? Who are the Valar? Who is that Elbereth Gilthoniel that people keep praying to? How did the Elf/Dwarf feud originally begin? And how exactly is Elrond related to Aragorn?
For the most part, it focuses on the Elves and their history, especially where it intertwines with the history of Men -- although Dwarves and Hobbits don't get nearly as much ink devoted to them. But in that story, Tolkien weaves together stories of earth-shattering romance, haunting tragedy, gory violence, good versus evil, the rise and fall of cities and kingdoms, and much more.
However, it's not really written like Tolkien's other works. It's more like the Bible, the Mabinogion or the Eddas. Tolkien didn't get as "into" the heads of his characters here, and wrote a more detailed, sprawling narrative that would have needed countless books to explore in depth. But while his prose is more formal and distant here, it still has that haunting starlit beauty ("Blue was her raiment as the unclouded heaven, but her eyes were grey as the starlit evening; her mantle was sewn with golden flowers, but her hair was dark as the shadows of twilight").
It's clear to see, while reading this, the extent of Tolkien's passion for his invented history. Someone who had a lack of enthusiasm could not have spent much of his adult life writing, revising, and polishing a history that never was. It's also almost frighteningly imaginative and real: It isn't too hard to imagine that these things could actually have happened. In a genre clogged with shallow sword'n'sorcery, Tolkien's coherent, carefully-written backstory is truly unique.
Casual Tolkien fans probably won't be able to stick it out. But those who appreciate the richness and scope of Middle-Earth should examine "The Silmarillion," a sprawling fictional history full of beauty, tragedy and love. A work of literary genius.