There's also one or two questlines in Kun-Lai that are pretty interesting like that.
1.The first is part-way through some of the Yaungol stuff where you have to break out some Shado-Pan dudes only to find one guy pretty much gone. His wife/lover sees this and gets emotional and vows revenge. Sometime later, you stop at a Yaungol village which has been totally decimated by its inhabitants who were possessed by the Sha. Sure enough after some quests, you find that the guy's wife had been camping up in the village and ends up possessed by the Sha of Hatred and you have to put her down.
2.The second is something to do with this swamp dude and his buddies. The Yaungol are messing with the swamp, so you do some quests to help him and his buddies get back to full health and take on the main guy tormenting them. Though the dude ends up being much stronger than expected and kills them off except for the guy you found to begin with. Eventually, you kill the Yaungol dude, the swamp dude gives you a reward and fades away...he died.
Those are TOwnlong Steppes. And yes, sad quests