Okay, at the bidding of a friend, I picked this book up in route to reading the Hobbit and the Lord of the Rings books. It's been a bit difficult (flipping to the appendix often to reference a name or map, etc), but quite interesting and amazing well written and detailed.
Without giving away any spoilers (I'm only on chapter 21), what did everyone else enjoy about it?
i got somewhat bored w/ the first third of the book (repeating over and over the creation myth of middle earth) and the last third (the lineage and migration of the elves), but rather enjoyed the stories of the middle third. i would have to say though that i'm glad i read the first and last thirds as they did illuminate the history and mythology of middle earth, but they weren't entertaining enough for me to reread. i have reread the middle third a few times.
i think that for most people i would recommend reading lotr before the silmarillion as then you will have a better context for understanding the silmarillion. and alot of the minutia of the silmarillion will be lost w/o that context. but anyone who reads the silmarillion will then be tempted to reread lotr w/ the fuller understanding they have of middle earth.