Personally, as dumb as I know this will probably sound, when I think about old Azeroth my mind immediately returns to a tiny quest called Until Death Do Us Part. It's started by a bitter Forsaken who wants you take a pendant to her husband's grave at the Sepulcher. If you only wanted to look at it in terms of game mechanics, then it's a Fed-Ex quest designed to get you across the ocean and questing in Silverpine, but even with all the improvements to questing today, it stands apart. It's a very long journey for a young character, and when you finally arrive at the Sepulcher and find the husband's grave, you realize you've come all this way to deliver a worthless trinket to someone who threw his life away on a hopeless cause. You turn it in and...that's it. There is no follow-up. There is no happy ending. There is, however, the feeling that there's more to the savagery of the Forsaken than meets the eye.
Blizzard is actually trying to move away from quests that emphasize text over cool visuals, and it makes me a little sad just because Until Death Do Us Part was, from a writing standpoint, a masterpiece of effective writing and quick exposition. I'm hoping that, out of all the quests that stand to get axed in Cataclysm, this little gem survives.