Original post: http://forums.worldofwarcraft.com/thread.html?topicId=24262356308&sid=1

World of Warcraft: Cataclysm will bring with it several changes to class talents and abilities. In this preview, you'll get a glimpse at some of the new abilities, spells, and talents in store for the death knight class, along with an early look at some improvements we plan to make to the rune resource system.
New Death Knight Abilities
Outbreak (level 81): Outbreak infects the target with both Frost Fever and Blood Plague at no rune cost. This ability allows death knights to apply diseases quickly when they are switching targets or when their diseases have been dispelled.
Necrotic Strike (level 83): Necrotic Strike is a new attack that deals weapon damage and applies a debuff that absorbs an amount of healing based on the damage done. For context, imagine that the death knight can choose between doing 8,000 damage outright with a certain ability, or dealing 6,000 damage and absorbing 4,000 points in incoming heals with Necrotic Strike -- the burst is smaller, but a larger overall amount of healing would be required to bring the target back to full health.
This ability is meant to bring back some of the old flavor from when death knights could dispel heal-over-time (HoT) effects. It also gives the class a bit more PvP utility without simply replicating a Mortal Strike-style effect.
Dark Simulacrum (level 85): The death knight strikes a target, applying a debuff that allows the death knight to copy the opponent's next spell cast and unleash it. Unlike Spell Reflection, Dark Simulacrum does not cancel the incoming spell. In general, if you can't reflect an ability, you won't be able to copy it either.
Rune System Changes
While we're satisfied with the way the rune system works overall, we're making a few major changes to the mechanics that will ultimately help death knight players feel less constrained. Here's the rationale behind the changes, followed by an explanation of how the new system will work.

• In the current rune system, any time a rune is sitting idle, death knights are losing out on potential damage output. By comparison, rogues spend most of their time at low energy levels, and if they're unable to use their skills for a few seconds, that energy builds up and can be spent later, minimizing the net loss from the interruption.
• A death knight's runes, on the other hand, cannot be used until they are fully active. If a death knight ever goes more than a few seconds without spending an available rune, that resource is essentially wasted. Because the death knight is pushing buttons constantly, it can be difficult to add new mechanics to the class because the player doesn't have any free global cooldowns to use them. We can't grant extra resources or reduced cost, because there is no time to spend them. Missing an attack is devastating, and it's impossible to save resources for when they're most useful.
• Additionally, each individual death knight ability has a fairly low impact on its own, making it feel like most of the death knight's attacks are weak. The death knight's rotations are also more easily affected by latency or a player's timing being just a little off. At times, it feels like death knights aren't able to take advantage of their unique resource mechanic, which can diminish the fun.
• The new rune system will change how runes regenerate, from filling simultaneously to filling sequentially. For example, if you use two Blood runes, then the first rune will fill up before the second one starts to fill up. Essentially, you have three sets of runes filling every 10 seconds instead of six individual runes filling every 10 seconds. (Haste will cause runes to fill faster.) Another way to think of this is having three runes that go up to 200% each (allowing extra "storage"), rather than six runes that go up to 100% each.
• As this is a major change to the death knight's mechanics, it will of course require us to retune many of the class's current abilities. For example, each ability needs to hit harder or otherwise be more meaningful since the death knight is getting fewer resources per unit of time. Some abilities will need to have their costs reduced as a result.

Talent Changes
Next we'll outline some of the death knight talent-tree changes we're planning in Cataclysm. This list is by no means comprehensive, but it should give you a sense of how we're intending each death knight spec to perform.

• One of the biggest changes we're making is converting Blood into a dedicated tanking tree. While we feel that having three tanking trees was successful overall, it's less necessary in a world with dual-specialization. In addition, the current breakdown isn't as compatible with the Mastery-based passive talent-tree bonuses we want to add (see below). We'd rather spend time tweaking and balancing one good tanking tree rather than having a tank always wondering if they picked the "correct" tree out of three possibilities.
• Blood seemed like the best fit for tanking. Unholy has always had a strong niche with diseases, magic, and command over pets. Frost now feels like a solid dual-wield tree with Frost magic damage and decent crowd control. Blood's niche was self-healing -- fitting for a tank -- as well as strong weapon swings, which could easily be migrated to Frost and Unholy.
• Our plan is to move the most interesting and fun tanking talents and abilities to Blood. For example, you will likely see Vampiric Blood and Will of the Necropolis remain, while Bone Shield will move over from Unholy.

Mastery Passive Talent Tree Bonuses
Blood
Damage reduction
Vengeance
Healing Absorption
Frost
Melee damage
Melee Haste
Runic Power Generation
Unholy
Melee damage
Melee and spell critical damage
Disease Damage
Healing Absorption: When you heal yourself, you'll receive an additional effect that absorbs incoming damage.
Runic Power Generation: This will function as the name implies, and the new rune system will make generating Runic Power more appealing.
Disease Damage: Unholy death knights will be able to get more out of their diseases, which are integral to the tree's play style.
Vengeance: This new mechanic is designed to ensure that tank damage output (and therefore threat) doesn't fall behind as damage-dealing classes improve their gear during the course of the expansion. All tanking specs will have Vengeance as their second talent tree passive bonus. Whenever a tank gets hit, Vengeance will grant a stacking Attack Power buff equal to 5% of the damage done, up to a maximum of 10% of the character's unbuffed health. For boss encounters, we expect that tanks will always have an Attack Power bonus equal to 10% of their health. The 5% and 10% bonuses assume 51 talent points have been put into the Blood tree; these values will be smaller at lower levels.
You only get the Vengeance bonus if you have spent the most talent points in the Blood tree, so you won't see Frost or Unholy death knights running around with it. Vengeance will let us continue to design tank gear more or less the way we do today; there will be some damage-dealing stats, but mostly survival-oriented stats. Druids typically have more damage-dealing stats even on their tanking gear, so their Vengeance benefit may be smaller, but the goal is that all four tanks will do about the same damage when tanking.
We hope you enjoyed this preview, and we're looking forward to hearing your thoughts and feedback on these additions and changes. Please keep in mind that this information represents a work in progress and is subject to change as development on Cataclysm continues.