Well, for me personally sex scenes in porn stories put me asleep, because more often then not they're essentially just a list of sex poses the author could come up with multiplied by the number of characters in the scene, and I fail to see what's entertaining about a list. Guro is a little better, because it has more extreme things happening, but in the end the point of things happening in the story is to feel emotions about them, and the point extreme things happening is to feel extreme emotions. Simply put: don't just write a story as a list of events, instead make the reader feel something about those events.