I will contend that the prepatch for WoW: WOTLK was cooler, even though it straddles the line between server maintenance and an expansion pack release. It was eight phases, one day each:
1. Plagued boxes start appearing in a neutral port town. Players are infect with the plague, and turn into zombies. The zombies spread the plague to other players. The only cure is to find a special healer, before it's too late.
2. The boxes start appearing in capital cities.
3. As the healers got taxed, the plague gets quicker. It's much harder to be cured.
4. The plague is now deadly fast, and undead citadels are now floating above the cities.
5. The plague is basically instant now, and the healers are essentially gone. All trade in the cities is breaking down, and it's starting to mess with players' ability to organize.
6. You get a quest to give a briefing to your faction's leader
7. The plague has been cured (at this point it's been seven days of bedlam, you can't get shit done in a city without being attacked by ghouls)
(Like a week later) 8. The citadels open up, and skeletal dragons and hulking flesh-abominations attack the capital city. The playerbase has to fight it off. The Lich King mocks your pitiful kingdoms and taunts you to come to his, in hopes of killing you and making you into new soldiers...
I have never been more hyped for a game update.