A fascinating, moving tale of Middle Earth and its people during the First Age.
The Silmarillion is the story of Tolkien's Middle Earth before Bilbo and Frodo, before the rise of Sauron, before the Age of Men. It is the history of that world, taken from its creation to the sailing of Eärendil into the West.
The Valar are described as holy because they follow the word of Ilúvatar, while Melkor is evil because of his rebellion and desire for the work of the Valar to be destroyed. That outlines good and evil pretty starkly right at the beginning, and as the history progresses there is a clear idea of right and wrong. When there is treachery it is not condoned, and selfishness and other such actions are not rewarded. Honor, love, and courage are some of the more prominent virtues displayed by the heroes and heroines.
As this is written as a chronicling of events, however, there are places where men commit wrongs (a man kills his friend out of anger, for instance) and there is no direct recompense; but neither are these actions smiled upon or swept under the carpet - they do reflect upon the characters of the people involved.
The Silmarillion is in many ways a mythology of a fantastical world, and so there is a lot of talk of the Valar, the Maiar (lesser spirits), and Eru/Ilúvatar. The story begins with a cosmogony - with the creation of the world. However, Tolkien himself said that he was not fond of allegory and his world-making, though it bears some similarities to the Genesis account, was never meant to be Christian. Eru, or Ilúvatar, who seems to be an eternal god, creates first the Ainur (Holy Ones) and commands them to sing. By their song they sing into existence the World; during the music, however, one of the Ainur rebels against the mind of Ilúvatar and decides to sing his own song in opposition to the rest of the music. For his rebellion Melkor, later known as Morgoth, becomes the enemy of Ilúvatar and the Valar.
The Valar, mentioned periodically throughout this book and the Lord of the Rings trilogy, are known as the Powers of the World. They are the Ainur who dwell in Arda (Earth) instead of with Ilúvatar, giving it its life; being, rather, gods of the earthly elements. These beings have a great deal of power and command the earth, the sea, the air, etc. They are also capable of creating just about anything, as is Melkor.
Twin Trees grow in Valinor for the protection of that place from Melkor, similar to the mystical trees from the Norse mythology and the Tree of Life of Eden. Later the three jewels known as the Silmarils, which are at the heart of the stories, are made from the light of the Trees; they are not magical, but they are powerful all the same.
There are immortal Elves in this story as there are in the rest of The Lord of the Rings, and there are evil creatures like Ungoliant the Spider. Enchantments and spells are used by some of the Elves.
There are many battles, fights, and deaths throughout the stories; the Valar war against Morgoth (Melkor) and he attempts to destroy Arda, once employing the use of the spider Ungoliant. He imprisons several people in his dungeons, tortures other people, and in various and sundry ways attempts to kill characters.
A man's hand is bitten off by a wolf. A woman is shot with a poisoned arrow and dies from the wound. One character is thrown over the side of a cliff, so ending his life. An Elf is taken by Morgoth and hung on a precipice by an iron band around his right wrist, and to get him down his friend cuts off that hand. Túrin Turambar slays quite a few men in his tale, including his dearest friend whom he thought was attacking him.
There are other instances of violence - characters dying or killing others - in the story, but this covers a good bit of it. While not graphic, violence is very present.
Drug and Alcohol Content
There are frequent mentions of marriage throughout the tales as well as of childbirth and conception, and there is also love. There is the tale of Beren and Luthien and how he won her hand. In the tragedy of Túrin Turambar a man marries his sister, neither realizing their relation; when she learns of it, she is heartbroken and commits suicide. There are a couple instances of nakedness in a nonsexual context, but nothing is described and it is only briefly mentioned. Nothing is graphic at all.
Crude or Profane Language or Content
Men swear oaths, but there is no profane language.
Most read The Silmarillion expecting another fantasy tale like The Lord of the Rings or The Hobbit. This is a mistake. It should rather be read as a history or a mythology of Tolkien's fantastical world, a story in the same vein as the ancient Beowulf, with war and romance, tragedy and love all intermingled throughout each section. Tolkien fans with a love of history will enjoy reading this and seeing how he used the mythologies of the ancient world to weave his own tale. Not only that, but it is fascinating to see the backstory for some of the characters in The Lord of the Rings - Galadriel, Aragorn, Elrond, and Gandalf, for instance - and get a better feel for Middle Earth. Certainly a worthy read for those who have read and loved Tolkien's fantasy trilogy.