This book continues with early drafts and finished versions of Tolkien’s epic mythology. In this book you’ll read the early tales of Túrin Turambar, Beren and Lúthien, The Fall of Gondolin, and the story of the Nauglamír. Just like in The Book of Lost Tales Part 1, the overall synopsis of the stories is roughly the same as in the final published version of The Silmarillion. In fact, I’d say the Book of Lost Tales 1 and 2, are far more easier read than The Silmarillion. One of reasons why I love the Silmarillion so much, is because how incredible complex the stories are. For example, some of the alliances and the connections between the characters is non-existing in The Book of Lost Tales. Not to mention, Tolkien’s additional work in elvish languages.

NO SPOILERS:
Not really a spoiler, Númenor is non existing in The Book of Lost Tales (so are the characters associated with it). Sauron doesn’t exist in The Book of Lost Tales either, but rather other characters play the role that Sauron had in The Silmarillion. Also the iconic geographical place of “Middle-Earth” is not referred too using that name.

To conclude, in my opinion The Book of Lost Tales feels more like a novel. Even though both The Book of Lost Tales and The Silmarillion are books of mythology and history. Thanks to The Hobbit and LOTR, The Silmarillion feels more like a historical account of the world. While, in the other hand The Book of Lost Tales does have it’s own unique ending. (Which completed Tolkien’s early mythology at that time)
By the time I finished reading this book, it was very clear to me how much of a drastic change or “extensions” to The Book of Lost Tales in The Hobbit and The Lord of The Rings had caused, to what evidently came to be the final version of The Silmarillion, which to me is the greatest book of all time.