As a raid level DK tank, I feel sorry for the other tanks getting this change. At the moment DKs, while not being underpowered in any way, play very counterintuitive at raid level tanking. We sacrifice using any blood runes, and refreshing deseases outside of outbreak due to the fact that runic empowerment will proc more death strikes, and using runes on anything but death strikes can kill you. "Fine", you say, "just spam deathstrike!" but there is an aweful catch 22 there. If we use a death strike prior to the boss' swing we get a very slight heal and a worthlessly weak shield, but if we use it after a boss' swing, we get a bigger heal and a much better shield. This is why death knight health spikes so much, but we heal that health back, unless a healer tops us off befor we can get in several death strikes. This is a common reaction for healers, the tank takes a large ammount of damage, so you use an emergancy heal, but in doing so, weaken the death knight for the next hit, in which this process is repeated untill the deathknight either dies, or the healer runs oom. This is why death knights are in general the least appealing tank to play or to heal, they are counterintuitive and require the healer to put too much thought into healing the tank (ie. "Does he have runes for deathstrike? Should I get a big heal ready just to be safe? Will I gimp his heal and shield, effectivly weakening his mitigation and effective health?")

TL;DR: Death knights need some major qol fixes befor blizz decides to force all tanks to play with this handicap