General Skill Changes
Blood Strike: The bonus damage this ability receives from diseases on the target has been increased to 50% per disease. This change was probably mostly to compensate for some of the damage nerfs to other strikes below, but there's also the possibility here that Blizzard's looking to simplify rotations a bit. Blood Strike has become, for Unholy and Frost, mostly a way to churn out Death Runes. Bumping the damage a bit makes up for some of the other damage nerfs and has a chance to make Blood Strike a bit less of a pariah.
It's worth noting that although the patch notes say damage is being increased "to" 50% per disease, we have to acknowledge that that would be borderline obscene, and they likely mean "by" 50% per disease to 18.75%, which is still a pretty decent increase.
Chains of Ice: Now reduces movement by 95% instead of 100%. The main effect of this change will be that targets of Chains of Ice will not have to re-issue a movement command to continue moving. This change shouldn't be too much of a concern, really. You can technically argue that it's not like other classes can't root (see Druids), but since Chains of Ice is meant primarily to be a snare rather than a root, it's not a completely unfitting change. Smart PvPers probably weren't tripped up by it before anyway, so we haven't lost much all told.
Frost Strike: This ability can now be dodged, parried, or blocked. Weapon damage bonus reduced to 55%, down from 60%. This was not an unexpected change. Frost Strike, especially if you manage to pick up that Sigil from Ulduar, is just plain devastating. Ghostcrawler's been making noise about nerfing it for some time now. As it is, the weapon damage modifier is still in place, so there's no reason to believe it won't still be a viable runic power dump, and the frost damage still ignores armor.
Icebound Fortitude: Cooldown increased to 2 minutes. It does suck that this is getting a nerf, but the fact remains that we absolutely dominate tanking. Almost any major boss encounter is made infinitely easier when a Death Knight is tanking it because we generally always have a strong tanking cooldown ready. So while we keep getting tanking nerfs, every time we continue to dominate. Icebound Fortitude is probably one of the cornerstones of our domination, so breaking up the rotating cooldowns method of Death Knight tanking even more makes sense. It still refreshes faster than Shield Wall, at least - not that it's always as easy as comparing two similar abilities from two different classes without context.
Frost Presence: 10% bonus health reduced to 6% bonus stamina. This nerf was probably primarily for scaling reasons. We've already hit Tier 8 armor wise, we have Tier 9 coming up fast, and it'll only go up from there. Easing back on the scaling now will help keep our power in check later. Overall, Death Knight do not have a problem getting high HP totals, so this nerf, while it will hurt, will hopefully still leave us comparative healthy next to other tank classes.
Dancing Rune Weapon: This ability now has a fixed duration of 12 seconds (which can still be modified by its glyph) and a fixed cost of 60 Runic Power. This is one of those uncomplicated changes I talked about earlier. Now, instead of waiting to cast Dancing Rune Weapon, you can set it and forget and use the remaining Runic Power for Death Coils as appropriate in your rotation instead of artificially holding back until you hit the right amount of power. That said, if the Unholy Blight change noted below ends up powerful enough, especially combined with Sudden Doom procs, we may see a rise in the amount of 50/0/21 Unholy builds out there too.
Veteran of the Third War: Stamina bonus reduced to 1/2/3%. See Frost Presence. Blizzard likely believes our health stacking will just get entirely too potent in Tier 9 gear. Considering Blood Death Knight tanks have been popular for their high armor and health for ages, it makes since they'd get a bit more targeted health nerfing. As I said before, this is something we'll probably need to test to know if the nerf's too much or not.
Blood of the North: Reduced to a 3-point talent. Increases Blood Strike and Frost Strike damage by 5/10/15%. There is now a 33/66/100% chance whenever you hit with Blood Strike or Pestilence that the Blood Rune will become a Death Rune when it activates. This is a nice buff that is probably mostly meant to free up a few talent point for the new Threat of Thassarian (see below.)
Lichborne: Duration reduced to 10 seconds, and cooldown reduced to 2 minutes. Considering how much Will of the Forsaken was nerfed in it's day, it's almost surprising it took them this long to do it for Lichborne as well. It still essentially acts as a spare trinket with the added bonus of providing some temporary immunity as well, and with the cooldown reduction. It might almost be considered an overall buff unless you've been using it to take down Warlocks in 11-15 seconds, I suppose.
Threat of Thassarian: New 3-point talent. When dual-wielding, your Death Strikes, Obliterates, Plague Strikes, Blood Strikes and Frost Strike have a 30/60/100% chance to also deal damage with your off-hand weapon. Off-hand strikes are roughly one half the effect of the original strike. Now here's the doozy. This is the promised returned to viability for dual wielding. While many, including myself, have been on record as saying that off-hand enabled weapon strikes would probably simply shift the balance back to dual wielding, the devs seem to be hoping that a slightly lessened effect on the off-hand damage will make up the difference. In a way, it does make sense if the combined damage manages to equal or come slightly under 2-handed strike damage instead of eclipsing it.
The murmur around the community from some is focused on the idea that the Frost tree isn't a big white damage tree, and since dual wielding traditionally thrives in part on high white damage, this talent would have been better in the Blood tree. In this case, the Frost tree may have been a deliberate choice on the part of the developers specifically for that reason. The white damage and strike damage increasers in the Blood tree may have made Threat of Thassarian just a bit too powerful. Frost also has the advantage of having a good amount of straight up magic damage that should, in theory, help dual wielding close the gap with two handers.
One other thing to note about this new talent is that it does not include Rune Strike. This has die-hard duel wield tankers a bit concerned, as it may leave dual wield tankers without the threat they need. Of course, threat these days is not a scarce commodity, so there's still at least some chance that the threat will be enough even without Rune Strike on ToT. It'll be something to test on the PTR, at least.
Of course, the big question for me, as a diehard 2-hand aficianado, is this: Will this ability eclipse 2-handed DPS? Blizzard seems to be banking on the idea that the relative dearth of other strike-damage increasing talents in Frost and the half-damage restriction on the off-hand will take off the edge and leave the field mostly balanced. Of course, balance decisions like this don't always survive an encounter with actual players, so this is probably where I'll focus most of my attention in PTR testing. I don't want to lose my big whomping 2-hander, after all.
Toughness: This talent now grants 2/4/6/8/10% armor instead of 3/6/9/12/15%, placing it in line with similar abilities of other classes. At this point, the tank nerfs are almost "nothing to see here, move along" proposition. But the fact remains that we dominate tanking in almost every possible scenario. At this point, nerfs are sort of expected. It is worth noting that some Death Knights think that this may drop our armor just a bit low when combined with the fact that talents such as Inspiration will turn into straight damage absorption instead of armor. This may be something that will merit further testing.