The most asked question seems to be, "Can he summon minions to fight with him?" because in the video, they show him reviving corpses or something to that effect. The answer is yes, you'll be able to summon minions, a la Overlord, to help you fight. However, according to Tom Chilton, one of the lead designers for World of Warcraft, "We don't want the Death Knight to be a sort of minion-based fighter. He's focused towards bladed weapons and smashing your head in."
They did at least let us know that they plan on bringing the Death Knight to all character classes, which caused someone to shout out "GNOME DEATH KNIGHTS FOR THE WIN!" Check out the official Death Knight FAQ from Blizzard by follwing that Read link. There's no release date yet, so you'll have plenty of time to dissect, complain, and drool in the intervening months.
Q: What are the features of the new expansion?
A: Wrath of the Lich King builds on the rich foundation established in World of Warcraft and The Burning Crusade, providing a wealth of new content for players to explore. The harsh, forbidding continent of Northrend, home of the Lich King and his undead minions, will be uncovered on the world map, and to contend with the new challenges found there, players will be able to advance to level 80, acquiring potent new abilities and talents along the way.
In addition, Wrath of the Lich King will introduce the death knight hero class to World of Warcraft. Once certain criteria are met, players will be able to create a new death knight character, which will start at a high level. Furthermore, player-vs.-player battles will reach a new level of intensity with the addition of siege weapons and destructible buildings, not to mention a new battleground. There will also be an abundance of new quests, dungeons, monsters, items, and recipes -- as well as a new profession, inscription -- for players to try out. The expansion will include some additional character-customization options for players as well. We'll be going into more detail on all of these features in the months ahead.
Q: How will the death knight class fit into the game?
A: The death knight combines martial prowess with dark, necromantic energies. Players might be familiar with the death knight from previously released Warcraft games -- most recently, in the campaigns for Warcraft III: Reign of Chaos and the Frozen Throne expansion, the former paladin Arthas became a death knight and wreaked havoc across Azeroth and Northrend before fusing with the spirit of Ner'zhul to become the Lich King. The death knight is the first hero class in World of Warcraft; once certain criteria are met, players will unlock the ability to create a new death knight character, which will begin play at a high experience level. We're currently exploring various options for how the death knight will play and the types of abilities at its disposal, and we'll be revealing more information about this new class as we get further along in development.
Q: Will the death knight have any abilities from previously released Warcraft games?
A: The way we portrayed death knights in past Warcraft games is certainly a source of inspiration, but we are still determining how best to capture that feel within the mechanics of World of Warcraft, and haven't made any final determinations on specific abilities.
Q: What role will the death knight play in groups and raids?
A: In general terms, the death knight can be considered a type of class that combines damage dealing and tanking, but naturally it will have an array of unique abilities as well.
Q: What races will be allowed to play death knights?
A: We haven't yet made a final determination about which races can be death knights. However, the class will be available to both the Alliance and the Horde.
Q: Will there be additional hero classes in the future?
A: Yes, we do intend to add more hero classes in the future, but right now our focus is on the current expansion.