Auto run. I'M STARING AT YOU, MINECRAFT!

This is a staple. It angers me when it is not present. (unless it's ingrained as part of the mechanics like Diablo. Yeah, I'm sure I'm not making sense.)
Little things. I'm very addicted to little things, and little details that game makers actually put in the game. Look up Skyrim's TV tropes and be amazed:
-Sit down in a tavern and the waitress will automatically approach you and ask what you want to drink.
-Skeletons only get jostled by Fus Ro Dah because most of the force doesn't actually hit them but simply passes through the empty spaces between their bones. Draugr, which have preserved skin, however, can be knocked back with the full force of the shout.
-Sneak into a room with bandits and drop something valuable on the floor, like a gemstone. The bandits will argue with each other over the object, and eventually attack each other.
ect.
Going to also say character editors. Nothing breaks immersion than having a choice of 3 heads and what color your skin is. Champions Online is the best paper doll game I've played yet. Bonus points if you get NPC reactions positive or negative for what your character race is (Oblivion?)
edit: dangit. Sorry