I spent my first few hours in the Wrath of the Lich King beta, and as there is no NDA, I'd like to tell you about it. As planned I made a Death Knight, and in the span of 4 to 5 hours leveled him up from 55 to 57, as well as out of his starting area, a little place I like to call Tortage.
Tortage? Isn't that the Age of Conan starting area? It is, and in Wrath of the Lich King it isn't really called that way. But taking a page out of the AoC book, the Death Knight starting area is an instanced region from which you can't reach the rest of the world until you haven't finished a series of "destiny" quests. And that plays just great, most fun I had in WoW for months. Your Death Knight starts with green armor and no talent points, and every quest gives you either a blue piece to replace a green piece with, and/or some talent points, and sometimes even some essential class skills. So by the time you finish your destiny quest series, you'll be fully clad in very good looking blue armor, have all the talent points you're supposed to have at your level, and all your essential class abilities.
And of course by being instanced, there are things possible that wouldn't be possible in the normal WoW, like the passage of time. For example when your destiny quest series is nearing the end, you're asked to go back to base by using a specific teleport portal. But that portal also transports you forward in time, to the same area, but looking much different from the advancement of events in the war between the Scarlet Crusade and the Scourge. Oh, and you're the Scourge, the epic destiny quest line tells how you'll eventually break free from the grasp of the Lich King. The whole thing contains some epic battles, with you doing various activities including steering a dracolich in a massive attack, or killing hundreds of enemy soldiers using their own canons.
Once out of the destiny quest line, you end up at Light's Hope Chapel in the regular world, and can start doing quests there. Or you can travel elsewhere. Fortunately all the flight paths are already available, you will not have to visit every zone in Azeroth on foot to tag all the flight points. I made my way to Stormwind City, used the new harbor there to get to Northrend, and learned the new profession Inscription there. I'll tell you more about that once I have explored that one more. But for a first evening in the Wrath of the Lich King beta it was a great success. I can only advise you that even if you don't plan on leveling a Death Knight up, do at least those 4 hours of destiny quest with him. It's well worth it.
Blizzard said that Death Knights should *feel* epic, and they certainly do. They also said that while feeling epic, Death Knights shouldn't actually be much better than existing character classes, especially the Warrior. Unfortunately they completely fail on that account. After 5 hours with the Death Knight I feel like deleting my Warrior (but won't do it because of his Alchemy). I can't say whether the damage output of a level 57 Death Knight is far superior to that of a level 57 fury Warrior. But his utility is far, far superior. How about a taunt that has a good range and not only forces the enemy to attack you, but also teleports him towards you? Finally a version of taunt that is useful for solo and PvP in WoW, as you can use it to keep enemies from fleeing, or even to pull. How about various abilities that convert either your damage or the enemies damage into healing, so you don't have all that downtime between fights that the Warrior has? How about spells that freeze the enemy to the ground or pelt him with spells from a distance? And that is just the start of the list. I don't know about the usefulness of Death Knights in groups yet, but I can already see they are much better soloers than Warriors, even in their frost "tank" spec. Right now census sites like WarcraftRealms show 12% of the players having a Warrior. I bet you that in a year that number will have dropped to 8% or below (if they properly update and don't count characters not played any more). Guilds will still need protection Warriors for tanking, but only a masochist would still play a dps Warrior if he can easily get a much better Death Knight. I sure hope that Death Knights are good enough as tanks in a group, because otherwise the only thing that is going to tank is the probability of getting a group together.