I don't remember where I first came across the Conan RPG, but it was the RPG that really opened up my
mind to the idea of a world where magic is not just a tool for flinging fireballs, there does not have to be a clear definition between good and evil and heroes do not have to be world saving noble warriors and wizards who all work together well.
I did not know anything about Conan or Lovecraft at the time, so it really opened up my eyes to a new world.
The game uses the D20 system, but most classes are combat oriented with the scholar being the only magic using class (though not all scholars have to become magic users) and magic being quite limited - there are few spells and most of them come with a heavy cost, such as human sacrifice, demonic pacts, allowing yourself to be brainwashed by a cult or corruption of the caster until they become possessed by a demon. Magic is not the flash bang type either - there are offensive spells but they do things like draw the heart out of someone's body.
While I think sticking the D20 system onto it wasn't perfect (it seems more apparent to me that the mechanics of a game should fit the flavour and sticking a generic system onto it loses some of the flavour. Engel is another example, where the German version used something that sounds way cooler than D20),
the Conan RPG really opened me up to other genres of writing and other ways to play an RPG.
It seems that the Conan RPG is not for sale any more, but you could probably find it second hand from somewhere.