Wrath of the Lich King is where the current paradigm for quests in World of Warcraft took full shape. Whether you played Horde or Alliance, you got to experience the events of Wrath from an entirely new perspective than questing had ever managed before. Even though there were still (and always probably will be) quests asking players to gather random amounts of (as an example) meat for stews or cannonballs, these quests were supplementary in nature.
The big-draw quests were elaborate chains that revealed lore about the world and the threat that it was now under. The Lich King's attacks on Orgrimmar and Stormwind during the events leading up to the expansion were bait in a subtle trap aimed at bringing players to Northrend. That's right: The Lich King attacked your cities entirely to get you sent to him. You. The player characters were the front and center reasons for everything. The Lich King desired nothing less than the finest heroes the Horde and Alliance had to offer, and that's exactly who they sent.
How did questing reflect this?
So come then, you heroes, in all your power and glory
The Horde starting experience in Borean Tundra is a good example of how the story directly involved you without necessarily having everyone fawn at your feet. Upon arrival, Horde players met with the Warsong Offensive's leader, Garrosh Hellscream. If you took part in the Hero of the Maghar quest line, Garrosh was somewhat respectful, but otherwise he was disdainful of new arrivals. However, upon taking up the task of quelling Scorge assaults on the Horde position, it soon became apparent that if Garrosh didn't respect you; Overlord Saurfang did.
The quest Foolish Endeavors is a brilliant example of quiet, elegant exposition. In it, Saurfang lays out the struggle to come in precise, elegant language. This world you seek to destroy is our home. Saurfang's involvement leads to your character's becoming, in effect, one of his direct operatives. It is in that capacity that you are sent to the Dragonblight and so become central to the events at the Wrathgate.
Alliance players aren't left out, however. From a quest in Howling Fjord that has you potentially run directly into the Lich King himself (and die for it) to saving the Ashbringer for Tirion Fordring, you're thrown into the fray almost immediately. The Alliance quests in the Dragonblight are arguably even more important for personal involvement, as you quickly become the favored instrument of the 7th Legion and eventually fight alongside Highlord Bolvar Fordragon himself to quell the lich Thel'zan. Either way, as a trusted figure instrumental to your faction's war effort, you end up asked to hold down the fort while the events of the Wrathgate unfold.
Time simply doesn't allow for a really detailed examination of how the game drives the character forward from the starting zones to the Dragonblight and the culmination we experience via the Wrathgate quests and the Battle for Undercity that unfolds. Sadly, the Battle for Undercity was removed with the coming of Cataclysm, so players currently leveling through 70 to 80 won't get to experience either faction's version. These quests absolutely put you as a player front and center in the events unfolding. I remember as I did the Horde version for the first time realizing that I was, in effect, the right hand of the Warchief in his negotiations with the Alliance and his decision to bring force to the ruined Undercity, as if I were Rexxar in the Warcraft 3 founding of Durotar. It was a heady feeling, marching into UC alongside Thrall and Sylvanas.
In my opinion, the first "act" of Wrath that ends with the Wrathgate/Battle for UC quests is simple brilliance and does exactly what the quest design in this expansion intends -- it puts you in the middle of unfolding events. You see the chaos unfold; your respective faction leaders directly turn to you to help unravel the knot they find themselves in. Any player who has gone through these quests should feel like a pivotal part of their world.
Secrets of Ulduar
While Ulduar itself is a side note to the unfolding story of the Lich King, Yogg-Saron's threat to the world was very real, and the use of Saronite by the Scourge (pretty much everything in ICC is made of the stuff) combined with the manipulations of Loken and the raid zone's events. The Storm Peaks and the 5-man dungeons Halls of Stone and Halls of Lightning do an excellent job of combining phasing and factional unlocking (the Sons of Hodir, in particular) to direct the story forward. Though there are some missteps (the daily quests get kind of odious at times), the ulimate experience of the Storm Peaks is aimed at getting players involved in the story of Ulduar.
From your first quests in the zone, you're directed to discover why the local Vrykul are kidnapping males from the local goblin town, which leads you to ally with a disaffected crone seeking to infiltrate this last bastion of loyal Vrykul warrior maidens in dedicated service to Thorim, one of the Titanic Watchers of Ulduar. Through your unfolding actions, you manage to achieve the near impossible and bring Thorim back to his resolve after centuries of mourning his deceased wife. You repair Thorim's relations with the Sons of Hodir, a group of Frost Giants loyal to another of the Watchers. You reveal that the other Watchers have all vanished from their places of power, help Thorim regain his trusted proto-drake mount, his warhammer, and confront his brother Loken ... only to discover that all you have done has been at Loken's instigation. You lure Thorim into Loken's trap all unawares.
Even your pursuit of vengeance in the Halls of Lightning is all part of Loken's plan. Warped by his proximity to Yogg-Saron over millennia, Loken is eager to die at your hands. In killing him, you directly trigger the Algalon protocol. That's correct: In attempting to avenge yourself on Loken for his manipulations, you doomed Azeroth.
This gives Ulduar as a raid zone a surprising amount of personal relevance, even if it is in effect a sidestep on the way to the final confrontation with the Lich King. You go in there to stop Yogg-Saron, yes, but also to fix the mess you yourself caused by leading Thorim into Yogg's clutches (thus giving him access to all four of his designated wardens and a chance at escape) and in killing Loken and activating the Titan's mechanism for judging Azeroth and reoriginating it if it fails said judgement. It's all astonishingly elegant.
Next week, the big misstep of questing in Wrath and how the Lich King ends.
While you don't need to have played the previous Warcraft games to enjoy World of Warcraft, a little history goes a long way toward making the game a lot more fun. Dig into even more of the lore and history behind the World of Warcraft in WoW Insider's Guide to Warcraft Lore.