Culture variations in other races than humans.
And when monster races consider themselves just as much at the center of their universe as humans do. It's a small touch, but I love when monsters call each other different things than humans.
Post or Pre Medieval settings. I especially love the era around neo-Imperialism and Age of Exploration. I think they both lend themselves nicely to adventures more, and the Bronze Age makes for nice epic adventures.
Magic being beyond comprehension. Having a neat list of spells and an orderly system turns me off heavily. It robs magic of its magic. A lot of times, I'll specifically avoid adding crunch to magic or magical things and leave it to narration. Things like Fae or Demons are not something you add stats to for victory in combat, they're something you out think or trick or compel.
I love confederations of city-states with dubious loyalty to some Emperor. From the outside it appears like a solid mass, then you look at the internal politics and find a swirling mass of constant civil wars and cloak and dagger acts as an nearly powerless figurehead tries to reign them in so they can get something done.