My spouse and I decided to watch The Fellowship of the Ring again, and as usual, I waxed slightly pedantic about Gandalf, and she had questions about technicalities. Age begins to tell, however, and I found I couldn't remember exactly how Gandalf got one of the rings of power. In any case, I decided to take another look at The Silmarillion as a refresher.
I first read The Silmarillion a very long time ago, and probably only once. While I recalled key nuggets from it about the Maia and the Valar, I also recalled that the interesting bits were few and far between, hidden among long dry passages with constantly changing names. Quite a lot of that is true, but overall, the book proved lighter and more readable than I recalled.
The Silmarillion and many of J. R. R. Tolkien's posthumously published works were collected and edited by his son Christopher, who admits up front that he's done the best he can to piece together disparate fragments into one relatively fluid whole. So, there are inconsistencies and gaps built in. The book is really a collection of several different stories, dealing with the creation of the world, the role of the god's servants (angel equivalents), the development of the Firstborn (elves), of the Followers (men), and of the rings of power (that tie in to Lord of the Rings). It's expansive, to say the least, with a larger scope even than a James Michener book. If ever an author was thorough in his worldbuilding, it was Tolkien. If you ever wanted to know more about Middle Earth, this is the place to start.
The Silmarillion has two major flaws. It's written in very dry, distant, academic language. Perhaps unsurprising in a creation myth by a Christian author, it has a biblical feel, full of 'begats'. It's hard to feel very close to any of the subjects (they don't really qualify as characters), and they don't generate much sympathy. It's a very different tone from that of The Hobbit, Smitth of Wootton Major, or Tolkien's more public-oriented works. The second problem is that, perhaps in a nod to verisimilitude in a book covering millenia, everyone and everything has multiple names - not just across languages, but among them. The book is full of phrases like "X, once called Y, and later called Z". The important land of Numenor is also called Westernesse, Westland, Anadune, Andor, Elenna, the Land of the Fallen Star, Akallabeth, Atalante, and Mar-Nu-Falmar. Ten different names may not be a lot for a long-enduring kingdom in real life, but it's quite a lot in a 300 page book. One at a time, the names are interesting and well considered, but overall, the effect is mind-numbing and confusing. Christopher Tolkien has done his best to provide a thorough index, and you'll likely need it to keep track of everything. Sadly, the two maps (in my old version) cover only a portion of the world (flooded before Lord of the Rings).
If you can get past the tone and the sheer flood of information, the story is fascinating. While the creation story has very decided parallels in Christian mythology, it soon wanders a little farther afield. It does answer some key questions from Lord of the Rings (who was Gandalf?), and if it doesn't answer them all, it's because that wasn't Tolkien's intent. He was creating a world, and Lord of the Rings is a very, very small part of it. The Silmarillion offers scope for dozens of stories just as interesting, or more so.
When I read this as a child, I found the book a slow, dry slog. As an adult, I found it much easier to get into - and much shorter than I remembered. The dry tone is certainly not a positive, but if you're interested in Middle Earth, there's a lot here to like. If you're interested in Tolkien's world, or in his famously thorough worldbuilding, set by a little patience, and give this a try.
Christopher Tolkien published over a dozen other (sometimes contradictory) fragments of his father's work on Middle Earth. Most will be satisfied with The Silmarillion, but for those that want more, there's plenty out there.