Death Knights are the new hybrid tanking class introduced by Blizzard in power leveling Wrath of the Lich King and offer some unique abilities in PvE and PvP to throw into the class mix.
While Blizzard has clearly stated that Death Knights will not replace Warriors as end-game main tanks, they are certainly viable as a tank, and more efficient at dealing with caster bosses then any of the other tanks with abilities like Anti-Magic Zone and Anti-Magic Shell.
With Druid¡¯s healing superiority over arena¡¯s in TBC with their high mobility, instant cast HoT¡¯s and stacking lifeblooms, death knights are going to be the equalizer, with abilities like Plague Strike, unfortunately it looks like Degeneration didn¡¯t make it through, but maybe a little overpowered.
Blizzard made a lot of changes with racials, and while many people say that you should only pick a race based on ¡°looks¡±, racial abilities should be another factor to look at if you are serious about end game play.