Christopher Tolkien recently edited and released Beren and Lúthien, a new book highlighting one of the central stories of the entire mythology. I was expecting this to be a novelization similar in form to The Children of Hurin, but I've heard, as Wikipedia implies, that it is more like an annotated collection of the different versions and fragments of the story that JRRT had written over the years. We've seen multiple such accounts already, from The Lord of the Rings to The Book of Lost Tales.
So what does this new book actually provide? Is there any new content that was not previously published, or is this just a repackaged anthology?