Overall, while I have loved snatches and pieces of music from past WoW efforts, I can say without reservation that this complete Wrath of the Lich King soundtrack is a cut above what has come before, and enjoyable, well-crafted music in its right.
My personal favorite is probably the Howling Fjord music, if only for one reason: Uilleann Pipes. I'm a sucker for them, and the music of the Howling Fjord uses them to incredible effectiveness. The stirring notes set the mood for the soaring vistas and majestics forests of the zone, as well as the struggle with the native Vykrul. Grizzly Hills comes in a close second in part because it has those same pipes being used to similar effect. What about you? Have you been listening to the new music? If so, what's your favorite music so far?