Zubon of Kill Ten Rats has been playing through Northrend lately, and it sounds like he's right around where my paladin is: working through the Wrathgate questline. The zombie invasion was the most important kickoff event for this expansion, but especially with what we've been seeing of Icecrown (spoilers there) lately, it looks like the events that went down at Angrathar might be the defining moments of Wrath of the Lich King. So much we're seeing in Icecrown and even beyond seems to be debris spinning off of the clash in that cinematic.
Zubon has mostly high praise for the storyline -- I agree that Borean Tundra and the Howling Fjord are preludes to the real anti-Scourge action you find in the Wrathgate questline. But then he goes one step further, and says that the end just shows how old Blizzard's game really is. Even while such an epic story is unfurling, graphical glitches and the realities of Blizzard's game (one of the phases is essentially an ongoing fight in which you personally have no effect) bring the experience back down. Wrathgate is certainly an epic event, and every indication is that we're going to be feeling its repercussions a lot in the next dungeon. But five years after launch, it's also a sign that Blizzard is pushing this old game as hard as they can.
Patch 3.3 is the last major patch of Wrath of the Lich King. With the new Icecrown Citadel 5-man dungeons and 10/25-man raid arriving soon, patch 3.3 will deal the final blow to the Arthas. WoW.com's Guide to Patch 3.3 will keep you updated with all the latest patch news.