If you read the Sil, then you know this story. If you haven't and have only seen the movies, (1) what is wrong with you and (2) Beren and Luthien are the couple that Strider sings about in Fellowship.
This book supposedly sets the story in a story mode as opposed to bits and pieces. But it doesn't really. It's more a collection of various parts of the story, rough drafts and what not. Some are in verse. There are illustrations by Alan Lee, which most likely are the real selling point of the book.
In many ways, it is a good source for an academic, but in terms of an actual story, nope. In some ways, it feels like a way to re-package something that didn't really need to be repackaged for the average reader, at least not in this format.
Lee's illustrations are nice though.