I read up to--I believe--the 9th or 10th book in the series before tiring of it, when I was in my teens. After reading Tolkien, Zelazny, LeGuin, and the occasional Thieve's World books, the Gor series was dense with detail, but rather poor in dialogue; making it parallel, I'd guess, George Lucas and his writing of Star Wars. I appreciate detail, so I enjoyed reading the early books. A new fantasy world, similar in form (if not style) to Conan or John Carter, and including sexual themes that are entirely absent from most fantasy novels I'd read--it interested my teen libido. No sex scenes to speak of, though there is more than enough sexual atmosphere, with all the focus on male-female interaction in such a M/s theme.
There's no surprise endings, nor really any unexpected twists. In a lot of ways, it reminded me of a 60s sexual escapism version of Ben Hur. The pace in the novels is quite slow--think Dune-like slow--and the dialogue is uninspired and plodding. I don't know...perhaps for my young mind at the time, it was just what I was looking for. I remember re-reading two of the earliest books more than once...Assassin of Gor and Raiders of Gor? Honestly, reading the Lankhmar books is far more satisfying to me, but despite the D/s themes in the Gor novels, it feels very derivative, on the level of how the Sword of Shannara was so derivative of The Lord Of The Rings.
It's very simplistic, and I saw it as escapism and enjoyable in an empty-headed way. Considering it dangerous makes no sense to me. If the crazies in the Gor-lifestyle community have a problem, it's that the internet allows mentally ill people to congregate and share ideas together. They are the problem, not the works of fiction they draw their philosophy from.