I've never been a huge fan of Conan. It isn't so much the idea of the setting, but Howard's writing style. I'm not a fan of the florid prose of that age. I'm not a big Lovecraft fan for much the same reason.
That said, I do like a lot of the implicit ideas in the Hyborean/Cthulhu mythos. The idea of ancient things from an incomprehensible beyond... the idea that learning about such things can lead you down a spiral of power and madness. That's good stuff. Also good is the idea that most monsters are human in origin.
Things I'm not as much a fan of that are typically included in such settings include social darwinism and rampant misogyny. Also, while I love the idea of madness and things from beyond reality being a source of magic, I have issues with them being the only such sources. There should be mysteries of the light as well as the dark... and it should sometimes be hard to discern between the two.
I think it would be awesome if there was a RPG setting that strongly supported playing a character who began by studying natural magic, but could be seduced to madness. This might include things such as herbalism, but it would also include the magical/natural laws that govern the powers of the unicorn and dragon. A natural mage could gain considerable power by harnessing these forces. Still, by studying them, he'd find inconsistencies... ways that the natural laws governing magic can be broken. Cheated. Exploiting these could expand his power. Doing so a small amount may not be harmful. Learning more, though, whether through texts of those who have studied such things extensively or through entreating entities that break such laws regularly, would be increasingly more dangerous to ones sanity.
I don't remember anything that really splits the difference in this way between your typical fantasy RPG and S&S-style power=madness. If you know of something, please let me know.