Spinksville, following up to an earlier post concerning a great lore moment in Vengeance Landing, concludes that as a Horde player, Howling Fjord has emerged as the single best overall zone in Wrath. The more I consider it, the more I'm inclined to agree with her. The Fjord has a mostly unified questline that slowly splits off into sub-plots concerning the Kalu'ak and Taunka, and the farther you get, the more you realize the impact your previous actions have had on that little slice of the world (and most of it's not good). As Spinks observes, it's a very immersive experience that does a great job of conveying both the moral ambiguity of the Forsaken's position, and the fact that Northrend's a continent without a lot of good options. "Forced to choose between the lesser evil and the greater evil," she writes, "... you had better hope that the greater evil is very bad indeed because it is the only way to justify the things you have had to do."
That said, I have to admit that Icecrown is also pretty tough to beat lore-wise (with the Matthias Lehner quests being a particularly good touch, and please don't click that link if you haven't run into him yet). I haven't yet played an Alliance toon through Northrend, and Spinks is also a Horde player, so I'd like to get some input from Alliance-side players too. Is the Fjord as good for Alliance as it is for Horde, or are your best questlines elsewhere? If you're Horde, do you agree that the Fjord was your best questing experience?