I, for one, am actually very excited for this book! Although I feel that PF has definitely developed class bloat, I kind of feel that this is a bit of an alternate options/classes book (at least under first impression).
What I am interested in is the stuff that hasn't been released for us yet: séances, eastern spirituality, etc. I'm wondering how this book will expand on the Mythos in Golarion and beyond. Will the Great Old Ones answer my call? Will the space beyond stars be elaborated upon?
I guess my greatest hope is that this book will unite the savory bits of Mythos that have thus far been baiting fans while bringing original classes into them. In our world, psychics and the occult are not considered in the true definition as "unknown", but as evil, mysterious and damning. (Yeah, it's biased, I know. Please just ignore that and move on.) I would really love to see this end developed.