Quests should be somewhat rare and not a means of getting exp as a main way to level.

Starting a quests should get you hyped for a good story with some cool cutscenes and intressting characters as well as pitting you against some intressting foes.

Have quests unlock futher quests/content upon completion as well as valuable ra/ex items rewards and reputation/fame for city factions or similar. I'd be fine with a decent exp reward as well adjusted to the difficulty and lenght of the quest, but more as a extra bonus and not the main reason for doing them.

The WoW, rift etc style of questing needs to go away, its dull and just a tedious grind, and we already have leves that supply this for the ones who enjoy such content as a means to level up.

Make quests special, make them cool, like side quests are in many great single player RPGs.