There are a whole load of new changes (22, to be exact) but a few of them really stand out. There's quite a bit of Blood love to try and make the spec more desirable at the endgame, one change being Heart Strike. While keeping its cost of one Blood Rune, it acts like a Cleave instead of a Haste debuff. It still hits harder than Blood Strike, too. That's pretty awesome!
One thing I personally don't see as a good change is switching Corpse Explosion to Runic Power, off of an Unholy Rune. Maybe I'm doing something wrong, but on my Unholy Death Knight I never seem to have enough Runic Power to use the abilities I want to use, and this won't help that. Of course, I don't have any spare Unholy Runes either. Maybe the spec needs some Runic Power generation love someday. To see the full list of changes, click through the link below.
In Ghostcrawler's words...
1) Rune Strike -- damage decreased from 200% to 150% but threat increased to 150% from 100%.
2) All multi-rune abilities generate 15 runic power.
3) Anti-Magic Shell -- cooldown lowered to 45 sec from 60 sec.
4) The healing of Blood Aura, Blood Presence and Death Pact has been doubled.
5) Bone Shield -- mitigation reduced from 40% to 20%.
6) Icebound Fortitude – now reduces damage by 20% instead of 50%. The amount of damage reduced increases with bonus Defense (to about 35% for 540 Defense, but it can go higher). The stun immunity is intended to be its primary role in PvP.
7) Frost Presence -- bonus armor increased from 60 to 80% and magic damage reduction increased from 5 to 15%. We wanted to reduce the effectiveness of cooldowns but bring up base mitigation to reduce damage spikiness.
8) Corpse Explosion -- damage increased substantially, added 5 sec cooldown, and changed cost to 40 runic power.
9) Heart Strike – we overhauled this ability. It no longer has a haste debuff but will now be able to strike two targets like a cleave. It still hits for more than Blood Strike, but you can still use Blood Strike if e.g. you don't want to break CC.
10) Horn of Winter -- now has no cost and grants 10 runic power in addition to its stat buff, but has a 30 sec cooldown.
11) Night of the Dead -- now grants 40/70% passive area spell avoidance to your pet in addition to its current effects.
12) Outbreak – this talent no longer receive bonus damage from Pestilence. The bonus from Plague Strike and Blood Boil has been increased slightly.
13) Bloody Strikes – the bonus damage from Pestilence has been moved here to help Blood AE slightly.
14) Pestilence -- no longer has a 10 sec cooldown.
15) Raise Dead -- now split into two spells: Raise Dead now raises a ghoul or pet ghoul (if talented). Raise Ally now raises a fallen party member (at no reagent cost).
16) New runeforge rune -- Rune of the Stoneskin Gargoyle (two-handed only) now grants 25 Defense and 2% Stamina.
17) Shadow of Death -- duration reduced from 45 seconds to 25 seconds.
18) Unholy Blight, Dancing Rune Weapon and Hungering Cold – cost reduced from 60 to 40 runic power.
19) Vampiric Blood -- in addition to its current effects, also adds 20% health temporarily.
20) Will of the Necropolis -- now reduces the damage of any attack that takes the DK below 35% health by 5 /10/15% instead of boosting armor when wounded,
21) Many death knight glyphs have been changed. In many cases the negative consequences were removed.
22) New death knight sigils are now available, primarily from vendors, including a tanking-oriented sigil.