Slow always means "it lost my attention" and I can't think of a better general description. My slow may not be your slow... but a story is slow if it lost your attention.

So one must ask, "how could I better keep my readers' attention?" Well, first, you have to define who you want as your readers. Because as old Abe Lincoln more or less once said, you can't keep everyone happy all of the time. If your iintent is porn, get to it. If it's a stoy with a plot and hot sex when appropriate, the set-up to the plot has to kick. Don't spend eons developing characters. They'll find themselves. But if you want to do a character study (with sex of course,) don't waste a lot of time describing what they're wearing and what the room looks like. I can make that stuff up for you, in my head. Just enough to get me started. Just those things you need if it's going to be important later... like the stereotypic redheaded temper. (And contrary to the current fad at some sites, of including a link to a photo array, no pictures please. Your hot clothed female isn't likely to match my definition of hot.)

In other words, slow is often too much stuff. I want enough to spark the imagination, then move on. I don't even need much in the way of "Arrrrrrrrrrrrrrghhhhhhh" when he cums... or "Noooooooooooooooooooooooooooooooooooooooooooooooo ooooooo" when she realizes she's about to be defiled.