My Thoughts: I'll be the first to admit I am not one of those TwiHard (or whatever they are called) fans. I didn't start the series until after the third book came out and still have not finished Breaking Dawn. I still found this insiders guide to be an interesting read.
I was concerned at first and didn't think I was going to finish it. The interview at the beginning with Stephanie Meyer is really long and I ended up skipping ahead. The sections on each individual vampire was very insightful and added to characters that we are already familiar with. It didn't make me like a character I didn't already but still interesting.
The family tree breakdown for the werewolves was well done and very detailed. The sections on the individual packs was set up like the vamps but I did not find it as interesting.
My favorite things were the illustrations. Whether fan created or other, they definitely made the book worth picking up. The end sections of foriegn covers, cars, music playlists, etc I found more entertaining than the rest of the book.
If you're a diehard fan you probably have already bought this but if you're curious do what I did and check it out from your local library.