Creatures Anathema is an excellent book! I would recommend this book to any GM that wants to terrorize the Acolytes that "get a little too big for their britches". Very good plot points and adventure "hooks" in this book.
This is an excellent game for many reasons! First, the ease of play due to the system. The Cortex system is very easy and flexible to use in any role-playing situation you might throw at your PC's in the 'verse.
The only minus about this book in particular is the iffy index that is included. (a small point indeed).
And if you love the Serenity Movie, this book can help you expand upon that universe and maybe provide you and your gamers a way to "re-write" the story!