First off, I really liked the first two parts, but this one just didn't have the same feel. No BE at all, and just very little description of what's going on in general. Some of the weird and erotic changes that do happen are simply glossed over, like they were added as an afterthought. A bulk of the action and actual prose are devoted to the sex scene, and even then, while reading, I didn't find it at all stimulating.
Honestly, this third part is too short, with not enough of what made the first two fun, nuanced, and interesting. Either this was written by someone else entirely, or the author quickly threw it together to end the story so he could focus on his extended universe.