This one was kind of a stumper, because I'm not sure what "intellectual" means (he says without a trace of irony). Does it mean complicated? Literary? "Narrativist"? What makes an RPG more highbrow than another?
So, I'll go with this one:
Ars Margica, First Edition. A fantasy RPG that didn't focus on dungeon crawling. "Troupe" play where players could choose between a cast of PC's, some grossly underpowered than the others. When I got hold of the game it just seemed so much more cerebral than what I was used to saying.
Ironically enough, I liked the first edition so much I basically passed on later editions as I saw the game get more and more bloated and heavily influenced by the burgeoning World of Darkness.
It's funny, in reflection, how much genuine affection I have for this slim little RPG.