This is the Hundred-and-fifteenth in my one-book-at-a-time bookshelf.
The Silmarillion is a jewel of a book (a pun for those in the know), prepared for publication after Tolkien's death by his son Christopher it is a collection of works, of which the title work is the most important providing as it does the dense kernel from which the more popular and accessible Third Age works derive. And it is dense and difficult going. This is not for fans of Lord of the Rings but for fans of Tolkien's Middle Earth in all of its rich landscape and history and language.
I bought this copy when it was published and I have treasured it and struggled with it over the years. When my kids ask me questions about Gandalf (was he always old? where did he come from? is he human?) or Elrond (is he an elf? where are they going over the sea?) or Dwarfs (what is their history?) I refer them to The Silmarillion (or the appendices) where answers to such questions can be found. And there are answers to these questions and more, a solid and rich foundation on which Tolkien built his other stories.
I won't pretend that The Silmarillion is a book for everyone, or that it doesn't lie unread on many shelves, but I treasure the insight it gives into Tolkien's world and I can't imagine not having it on my bookshelf.