Love what you've done with the smell, really. The little air freshener attached to the runeblade is a nice touch. Now that I'm in the beta, I've had the opportunity group with -- conservatively -- billions of you. I've healed a lot of Death Knight tanks, and tanked for a lot of Death Knight DPS. Most of you seem like cool people, so I say this with sincere love in my little Druid heart and a touch of worry over what will happen in November:
Most of you are awful.
I don't wish to be needlessly cruel here, mind you, or to overlook that the class is still new. Blizzard endlessly tinkers with you, so it's not like your rotations haven't changed, or your talents and skills are stable. And I know you're not coming to Northrend with a bank full of awesome gear from Burning Crusade. This isn't about your wearing greens or using the wrong attack or tanking rotation; I'm not even going to bother with the theorycraft surrounding the ideal DPS rotation until Wrath actually ships. But I'm seeing an awful lot of you running around playing as if...almost as if...you haven't played a tank or a melee class before. It's uncanny. But when I switched from playing a balance to a feral druid more than a year ago and knew nothing about playing a melee DPS/tank, I made all the mistakes you're making right now. Help me help you!
First things first, Scooter, and most importantly -- please stand behind whatever mob you are DPSing at all times. Where you are relative to the mob doesn't make a jot of difference when you're ranged DPS, but it's everything to melee, for several reasons:
BETTER DAMAGE: You will always do better DPS behind the mob, as they can parry, block, or dodge your attacks while you're in front of them. When you're behind them, they can only dodge. If you stay DPS, you want to stack enough expertise on your gear to overcome this dodge (in current BC raids, this is 26 expertise/102 rating, or enough to overcome the estimated 6.5% dodge chance on the part of a level 73 mob). While you won't have to worry about this too much while you're leveling up, a good number to keep in mind is that each point of expertise is 0.25% less dodge or parry on the part of the mob. If you're religious about staying behind every mob you DPS in a dungeon, you will never lose damage to a parry, and the expertise you manage to get on your gear will be functionally equivalent to +hit until the mob's chance to dodge has been pushed off its avoidance table.
DON'T WTFPWN YOUR TANK: There's an even better reason why you never want your attacks parried; a successful parry usually speeds the next swing of every mob and player in the game. Elitist Jerks has the numbers on it here if you're interested, but as a quick summary, a successful parry will cut the time to your next swing by 20-40% unless you've only just finished hitting them. This is true for every player and mob in the game with the current exception of Mother Shahraz in Black Temple and Brutallus in Sunwell (they're perfectly capable of destroying tanks without this mechanic, thank you very much). Over the course of a trash pull or boss fight this adds up to a number of additional hits and damage taken.
Mobs can parry anybody's incoming attack, but their hastened counterattack will always hit their present target -- your tank. Tanks can't avoid the damage spikes from their own attacks being parried unless they're packing a ton of expertise (which is currently very difficult for most tanks outside of Tier 6 and Sunwell). They can, and should, avoid the counterattacks that result from a melee DPS being parried, because that player should never be in a position to be parried in the first place. Every raider has a nightmare story about the tank who got wrecked while repositioning or rotating a mob that was still being auto-attacked by melee DPS or Hunter pets. Yes, Hunter pets can trigger parries too, but they're much less likely to do this nowadays as they automatically position themselves directly behind a mob when they don't have aggro. As one of the hunters in my guild used to observe, if in doubt about your location as melee DPS, stand on top of a pet.
HERE BE DRAGONS: It is very common for mobs to have a frontal cone attack or cleave. While Blizzard has mercifully removed 360-degree cleaves (though not Whirlwind) from mobs in the game, you risk getting very damaged or very dead if you're in front of the mob. Let the tank take that damage; it's their job. You're already vulnerable enough as melee DPS, which often gets hit by mobs' AoE attacks anyway.
So. Are you safely behind the mob now? Excellent! Stay there. And always tell your tank if they've positioned the mob in such a way that you can't get behind it or you'll pull the next mob pack in doing so.
AGGRO MECHANICS: if you're coming to a Death Knight from a ranged DPS class, what you may notice quickly (especially if you're using a crit-dependent build) is that you pull aggro faster than you did earlier. This is because ranged DPS gets an additional 20% aggro buffer that melee doesn't. In melee range, you will pull aggro at 110% of the tank's threat; ranged will pull at 130%. Unless I've missed something major, you don't presently have an aggro dump, so you're in the same boat as Enhancement Shamans and DPS Warriors. While tanks should have fewer problems holding aggro in Wrath, you are still better off giving the tank a few seconds to establish solid aggro on a large mob pack, especially if you intend to use Pestilence or Blood Boil. Don't take your cue on when to start DPS from a Rogue because Rogues can afford to ride the aggro threshold until it becomes desirable or necessary to Vanish.
SOMETIMES YOU ACTUALLY WANT AGGRO: Death Grip is your friend in the event of a runner (something that seems to happen less in early Northrend dungeons, but I'm sure we'll see it) or a mob that's taken off in search of the healer. It's also your friend if an inexperienced tank hasn't line-of-sighted a caster mob and there's a patrol nearby. Even if you're not specced or geared to tank, you are wearing plate and can lock down a mob or two until the tank can recapture aggro. Most Death Knights I see in the beta right now are leveling Unholy and have access to Bone Shield and the Anti-Magic Zone, but all of the talent trees have mitigation or avoidance talents that you can and should blow in the event of an emergency.
I'll be continuing this with another look at Death Knights as tanks soon, but these are the problems I've seen in (to be frank) many, if not most, new Death Knights DPSing in Northrend dungeons.