After several weeks' worth of "effort," I finally finished reading the Silmarillion. As anybody who has even attempted to read the Silmarillion will tell you, this is not an easy book to read. Except for a few brief passages, the book is not presented as a dramatic narrative. This makes it nearly impossible to "lose yourself" in the story.
Rather than the dramatic narrative structure used in most works of fiction, Tolkien presents the Silmarillion in the manner similar to that of Edith Hamilton's Mythology. The tales presented in the Silmarillion are the myths and legends of the Quendi (Elves). The story spans several millenia, beginning with the creation of Eä (the universe) and ending with a brief version of the War of the Ring.
This book illustrates one of the greatest difficulties facing an author of fantasy: setting. For stories set in some version of the world that we inhabit (past, present or future), most of the setting already exists, waiting to have characters and story imposed upon it. Fantasy, however, presents the additional challenge of creating the very world in which the story and characters exist.
Okay, this isn't always true. There are Shared Worlds out there, but these are practically exceptions to the rule (somebody still had to create them). From the whimsical Discworld to war-torn Westeros, most of the world's fantasy authors have created their own worlds in which to spin their tales.
By the way, if the worlds I just linked to are not familiar to you, I have some excellent books to recommend.
Part of what sets Tolkien apart from the others is the depth with which he created Middle-Earth. Not only did he create a world and populate it, he gave the peoples of Middle-Earth a deep, rich history and mythology. This history and mythology, which shaped Middle-earth, are very nicely detailed in the Simlarillion.
My rating? I give it ten wrathful Valar.