Blizzard drops some Death Knight details in a Q&A with the design team for World of Warcraft: Wrath of the Lich King. The Q&A explores the role the new class plays in game lore as well as your adventuring party. The player character Death Knights have rebelled against Arthas, joining the Horde (yay!) or Alliance (boo!) to help take down the vile Lich King. Rather than being powered by rage or mana, the Knights will use a completely new Rune System to power their offensive magic and abilities. Unable to use shields, they'll rely on magic to help them mitigate damage and generate threat, culminating in what Blizzard hopes will be another fun tanking class that will make Warriors feel even more useless than they already do.
Death Knight Interview [World of Warcraft]