My own two cents:
I like at least moderately plausible situations. Not saying that what happens should be the most ordinary, mainstream case, but I'm not into "what a whale of a tale" stories. There must be some explanation why the characters are about to engage in "spicy" behavior. Thus, I like some kind of "backstory". However this backstory should not be long winded.
I dislike reading stories with what seem to me like product placement (though unpaid) or unwarranted description of some kind of lavish lifestyle. I understand that some people fantasize about the lives of the likes of Kim Kardashian, but I'm uninterested. I don't like either obsessive repetition of certain characteristics (e.g. reminding the reader even 15 lines that the female protagonist has a certain breast size).
When I write, I usually do not include nonessential physical description. If for instance I write about a situation where a wife ends up getting a digital rectal exam and prostate massage to her husband, is it necessary that I include a detailed description of her hair, breasts and so on? Perhaps I should avoid that, so that readers can more easily project themselves as the wife or the husband.
Instead of physical detail, I'd rather include psychological elements. Does the husband feel ashamed? Does the wife feel exhilarated, and why?
Some stories in the library, I think, were overextended. The problem when writing about sex is that it gets repetitive after a while. Many authors go for the repetition, but there is a limit to what one can do around the same scene before being boring, and some go for adding increasingly artificial and/or implausible new acts. I think one should know when to end a story.