This book is pretty good if you are already familiar with Whedon's work. I love Buffy (it's my favorite show of all time), I like Angel very much, I loved the first Avenger's movie and really liked Cabin in the woods. I haven't watched some of the other shows, movies and comics this book talks about, but I still enjoyed it very much. I know feel the need to rewatch Buffy and Angel again (for the Nth time). I'm watching Firefly because of this, and I'm interested in Dollhouse as well.
So basically, if you're a fan of Whedon's, you will enjoy this.
I recommend it.