Finished reading The Book of Lost Tales Part 1 (Volume 1 of the Complete History of Middle-Earth). Some parts were considerably boring, but overall I'm glad I bothered to go to the end. Now to Part 2...
I planned to, but then started the Lost Tales, and it said they rendered the Silmarillon obsolete. I do want to see how the Tale of Tinuviel is dealt with though- the Commentary from Lost Tales II talks about skipping a whole section with Sauron the Necromancer.
That's because the Silmarillion is more like a "great history" of Tolkien universe: It cannot be much in-depth on the arguments. Just to say it, if I remember correctly, all of the LoTR is written in four or five pages.