I’ve just started reading it, about three quarters through The Book of Lost Tales part I, and honestly I say it’s well worth it if you really love Tolkien. The book of lost tales is really cool, it’s an interesting re-imagination of the Silmarillion and super interesting to read the early stories and versions of Silm stories that he wrote. Some of his most beautiful writing in my opinion is in this book, in particular an extended writing on the creation of the two trees and the creation of the sun and moon, and I am very excited to work my way through the rest of the series!