If you don't know, this cinematic triggers when you turn in a quest, both for the Horde and for the Alliance. The quest line ultimately leads to an assault on the Undercity, the Horde and the Alliance each going after different targets within the city.
The questline also has some great insight into King Varian Wrynn and a smattering of other things, but I'm not here to ruin the entire line for you. Just watch the cinematic. Oh, you did already? Well watch it again.
Both sides of the fence, Horde and Alliance, have said their respective heroes at that battle went down like chumps. I don't think that's true at all. Highlord Bolvar lead the charge and called out the Lich King. That takes stones, even if he didn't go down fighting. Huge, massive stones. Saurfang the Younger got one-shot, sure, but he took a swing at Arthas. He got punked, sure, but that takes stones, too. They went down hard, but they weren't cowards by a longshot.
Final note? Grand Apothecary Putress has an awesome supervillain cackle.
[ Video via MMO-Champion ]