I was very dissapointed in the regard of failing quests. Considering the fact that the only way of getting experience is by completing quests (which I like, though probably would do it based on objectives) you have to be super careful on what dou you consider as a failed quest (if there is any way to fail a quest at all!)
The concrete example in the beta. In the cat and mouse quest, I talked to the mobs, then go in to the inn and decided to fight the thieves and kill them, then I go out and fight the mobs and kill them too. What is my surprise when I see the quest failing negating me the exp reward. In my opinion that was disappointing, cause I resolved the quest in one way (killing both parts). I think probably money reward has to be negated but not the exp reward, since the quest got to a conclussion.
I think that making quests to fail or give different amount of experience depending on how you solve a quest, considering that it is the only way to get experience, is a design mistake that has to be addressed asap. (Sorry for being melodramatic, but I really think so). Either create other experience sources or make quests not being able to fail (just resolve them in different ways).