The Death Strike hotfix is bugged.

I think it may only scale to up to two diseases.

As several players above demonstrated, Death Strike ignores the third disease if you are Unholy and have a third disease. It does more healing with two diseases up than with one disease or no diseases up.

We lowered the healing done quite a bit. It appears to be working correctly.

If Frost and Unholy never Death Strike again, then we might consider a different implementation. Perhaps Death Strike heals similarly for all specs, and Blood just does more damage (but not more healing for that damage).

When there is a contention between quality of life issues and being overpowered, the latter always has to win out. We're not going to let an ability be overpowered for one spec just because nerfing it makes it weak for other specs (especially when the other specs have options to use other abilities or even respec).

Death knights have been at the top of the food chain for a long time. We're not trying to nerf them into oblivion, but if you're used to being an indestructible juggernaut, life might feel a little different for you in 3.1.

Some clarifications:

We don't think Death Strike was overpowered for Frost and Unholy. We'd like to get it in a place where those DKs can use it again. To do that we need to make some changes that will take a little longer to get in place. But we can't make it overpowered for Blood in the meantime.

We don't think the damage portion of Death Strike was overpowered, even for Blood.

Death Strike's healing being overpowered for Blood was not just a PvP issue.

We will read and consider good posts, as always. If using terminology like "knee-jerk" makes you feel better about being nerfed, that's up to you, but you usually don't see vocabulary like that used in good posts. Calling us names won't get a nerf reverted, and will likely get you banned. Be adults.

Q u o t e:
Otherwise, I want you to show me in this thread where someone asked to be an indestructible juggernaut.

Not many players asked to be indestructible juggernauts. Once again, the players didn't do anything wrong here, but DKs were overpowered in many aspects of the game, which was our fault. We made some changes over time, but it took the re-orchestration in 3.1 to really get DKs where we want.

My comment was in a response to some of the other comments that said things like "Now I can't solo 5-player quests any longer! LOL!" It has been our experience that when players have been playing a overpowered class that it does sometimes take a period of adjustment when the class is at more reasonable power levels. That's not intended to be a sarcastic comment. It really is true in my experience.

While we don't balance around QQ, I have noticed a perception in the forums that we are somehow handling DKs with kid gloves. We certainly didn't make any nerfs just to prove a point, but I also want to be very clear that no class is going to be able to escape nerfs when we think it's necessary.

Saying we should have made the change on the PTR really isn't relevant. When we think a change is needed, we are going to make it. Yes, it would have been great if we had changed it on the PTR. We didn't. That doesn't somehow mean we missed our chance and can't make changes when they are warranted. We went through very similar feedback with the Conflag nerf. We are going to make changes, and sometimes quickly.

I know it sucks to get nerfed. Believe me, it isn't a fun part of the job. But it is a responsibility we owe the game.

I updated the sticky above to reflect that we made another hotfix to Death Strike. The new model will give us more control over how much is healed. I quoted that post below.

There is a limit to how much we can (or are willing to) change through hotfixes. If there are other issues that we haven't changed yet, it could be that we technically can't make a change at this time. We have to handle it on a case by case basis. This was a relatively easy and low-risk fix. Not everything is.

Q u o t e:
UPDATE: We have since made another hotfix to just change the way the healing works completely. It now heals 5% of the death knight's health per disease on the target, up to a max of 15%. This should allow Frost and Unholy to benefit from Death Strike healing while letting Blood benefit from extra Death Strike damage. The tooltip will not reflect this change until we can patch the client.