After having looked at the masteries for healing, and concluding that they're pretty core- enhancing and fair, it's time to look at the tanking masteries to see if we can draw the same conclusions or something else entirely! Yet again, this information comes from wow.com.
Each time you heal yourself via Death Strike, you gain 50% of the amount healed as a damage absorption shield. Absorb increased further by mastery rating.
This is from speccing into the Blood tree. That Blizzard intended to make only one tree really viable for tanking is no news, and it will be really interesting to see how death knights will respond to this. One of the big charms of being a death knight, and in my opinion also one of the big problems about them, was the possibility to easily switch between tanking and dpsing. This meant that some thought they could be tanks just by switching to frost presence, but it also meant a unique way of tanking. It's also sad that Blizzard are removing this feature of Death Knighting (it's a real word) just because they're actually too lazy to keep on balancing the trees to work both as dps and tank-trees at once. They simply bit of more than they could chew with their vision for death knights, but I think it's sad they're giving up and turning Death Knights into this standard solution. As for the mastery, it's hard to say how much a blood Death Knight will be using Death Strike when tanking, and how much 50% of one Death Strike will make a difference. Considering the mastery requires it one can assume it will be part of the standard rotation and used as often as the runes allow for it. And as always, absorbtion is awesome for damage reduction so this could turn out to be really good, probably alot like Savage Defense works for druids today.
Increases the damage absorbed by your Savage Defense ability by 32% and increases the damage done by your Cat Form bleed abilities by 20%. Absorb and damage increased further by mastery rating.
32% sounds like they've really given this particular mastery some extra thought and balancing. I wonder why everything about druids always has to be so damn exact? Every other class gets "10% increase to X" but druids always get like "13,5% increase to X". Doesn't that say something about the problems with the class? I certainly think they do. It's like druids are theorized around fours different systems - casters, healers, tanks and melee - and therefor none of them work well because they always have to work with eachother in a way that is just not possible. I get the feeling that whatever they thought they needed to fix with Death Knights by making one tree the official tank-tree, they should've done long ago with druids. Ok, maybe I'm putting too much into this number, but it's really symptomatic about druids. One could also discuss how good Savage Defense is anyway, and this counts for the Death Knight Mastery too, since you need to be able to actively hit a target to benefit from the ability at all, something a tank might not always be able to do.
Increases your chance to block melee attacks by 16%. Block chance increased further by mastery rating.
Yet another uneven number, and I don't know why they specify melee attacks either. Is there something else that one can block? Maybe it's just to not confuse anyone, or maybe it's because they're changing how block works in Cataclysm, I don't know. I'm no fan of block, never have been. Block used to suck so much they simply just doubled (I mean like doubled!) the amount of damage that block will reduce. But it's still pretty sucky. Bosses in ICC can easily hit for like 25k and reducing that by some 3-4k now and then just seems so lame. And it doesn't do anything for magic damage at all, so realying on it too much isn't going to keep you alive against those Frost Breaths.
Increases your chance to block by 10% and your chance to critically block by 10%. Chances increased further by mastery rating.
Yet another block mastery, which doesn't suprise me since warriors always have been all about blocking and Blizzard will never ever change that, any less than they will remove totems for shamans (not that I want them to do that though). This is slightly more personal than the paladin mastery with the increase to critical block, which I assume is about the talent Critical Block. It could also of course simply be some new feature to blocking coming in Cataclysm, I don't think so though. Critical Block gives a chance to block double the normal amount (double again!) and this might actually make block become decent if it's up often enough. Then it will eventually just turn into working like extra armor, which is boring but efficient.
Overall there are two different types of masteries for tanks, the absorbers and the blockers, which is in line with how Blizzard is having the tanks work now. Absorbtion has historically always been vastly superior to blocking, but Blizzard are at least adressing the issue and trying to improve block. It's interesting to note that Death Knights, who can't block at all, were the tank of choice in the beginning of wotlk because of their great capabilities to absorb damage. Same thing with druid tanks in BC. Since then things have evened out quite much, and I can't really say that one tank class is superior to another anymore, not as it used to be anyway. I really don't like block as it is today. I don't think they should remove it as I like the general idea, but they definitely have to make it a more viable tank stat. How many tanks out there ever chooses block rating on an item over dodge/parry or stamina? For threat maybe.
On the other hand the two absorbtion masteries require the tank to be able to strike the target for it to be useful, something that is not required from block. Block is useless against magic, but a death knight/druid out of range of it's target won't benefit at all from their absorbtion masteries. Maybe these things will even it out between block and absorbtion in the end. I suppose that is what Blizzard is trying to find out now during Beta testing.