We need a storyline where we don't come out as the heroes. We need a whole expansion with this concept. Cataclysm is kind of pointing at that theme, but we need it to a greater extent.
For example, we could've lost to the Lich King. Everything we know would have been destroyed, cities and heroes. We spend the rest of the expansion fighting to regain back the things and lands we lost. This scenario would have had to start at the beginning of the expansion. As in the first raid boss would have been Arthas, we lose, then the story plays out as all of Azeroth is overrun.
The game needs to be turned on its head. We have to get away from the theme of: Hey look there's a bad guy, let’s go send our attack force to his footsteps and eventually kill him. It's too predictable and expected.
Again, Cataclysm seems to be going towards this idea, with Azeroth being attacked directly and changed for good. However, its needs to be done 100%. I'm talking Deathwing having control of everything, and we are held as slaves throughout the whole expansion. The play experience is us living in enemies cities, doing what they want. There are no more Alliance and Horde capital cities, no sanctuaries. We eventually form pockets of resistance, and form a formidable attack force. We start to have small encampments of freed alliance and horde forces. The raids are US defending against enemies trying to destroy our bases. Think role reversal. We sit inside the fortress/castle and our job is to defend against those people seeking to destroy us. Of course, the enemies will be computer controlled, just like raids now, but we basically just switch sides for the sake of the story. Then we eventually take out Deathwing.
Anyways, this is just my idea. I know it’s too late for this expansion, but perhaps the next one. We just need something different.