All right, I admit it; I read these books (the first few, anyway) when I was a teenager. John Norman's "alternate-Earth" is one of those series that every SF/fantasy fan (or at least, every guy) has probably read, but no one wants to admit it, or else you have to layer lots of disclaimers, like I'm doing. Yes, they're horribly misogynistic, cheesy, and just badly written, for the most part, and the most memorable thing about them is the Frazetta covers.
That said, the first three or four books were fairly typical swords-and-sorcery* in the tradition of Edgar Rice Burroughs's John Carter of Mars
. There was slavery, yes (and it wasn't just women being enslaved), but the naked slavegirls were an almost incidental part of the world; there was just enough mention of them to be titillating to the teen boys this series mostly appeals to. Most of the story was about Norman's self-insert Gary Stu hero fighting evil warlords, riding giant birds, and eventually, discovering the true masters of Gor.
Somewhere around book five or six, maybe (I don't know exactly; I never got that far into the series and have only skimmed later books), Norman seemed to abandon plot entirely in most of his books, and every new Gor novel became an extended S&M fantasy in which the author rants about how feminism has emasculated Earth society and every woman's true heart's desire is to be a man's possession. And he goes on for page after tiring page in this vein.
I maintain the first few Gor novels are readable if you're really into the genre. But the series goes off the rails pretty quickly, so if you're caught reading the later books, you deserve all the sneers you'll get.
* Strictly speaking, there is no sorcery: there's no actual magic on Gor, and later on we find out about advanced alien races, so technically, this is a sci-fi series, not fantasy. However, the tone and the setting is much more S&S fantasy than sci-fi.