I've had the pdf for a bit but recently received my hard copy of Lusus Naturae. Reading through this has inspired dozens of ideas for a new campaign just this afternoon. The physical book is very good quality, but the material is, in short, spectacular.
Rather than being just a collection of creatures, the book weaves a complex tale of possibilities by the creatures referencing each other. The party might encounter the Oocytic Warden or Elana Suur ... which will invariably lead to a search for Davinia Marrow. Of course, that will tie into encounters with marauding beasts that portend the coming of the Mallison. On top of everything else, there is a sweet monster generator in the back few pages that create more than just a set of stats, but horrible monstrosities with motives and style.
Rafael Chandler kicked some serious ass putting this together. I'm going to have to get a hard copy of Teratic Tome too. Maybe Pandemonio as well. Get your hands on a (legal) copy - this guy deserves your loot.