I could leave it at that, but ok ok, let's
To see exactly what I'm referencing, you can read the posts about the changes at MMO-Champion.com.
First, the tank change.
I had a long discussion with a friend who really was disappointed with this decision. He really liked being able to tank in all three specs. I think Blizzard worked very hard and made tanks of all three flavors 'viable.' However, it became clear that of course DK theorycrafters would try to find the 'best' tank spec and unholy was not it. Blizz still managed to keep blood and frost somewhat decent, but overall, it was indeed annoying to be selecting a tank spec, working your way down to that juicy talent deep in a tree, and have to spend most of your points on dps abilities. And of course vice versa (speccing dps meant avoiding those 'useless' tanking talents in every tree). So all in all I'm in favor of the change. Blood does indeed have the most unique feel for tanking. If it's not going to be a shield based tank (and I really realllllllly hope they don't create a 'prot' DK talent permitting shields), then self-heals is a pretty cool mechanic. They can really devote the tree to providing some cool tanking talents, and maybe even a couple of different tanking approaches within the tree. Putting more tanking abilities in the tree may also mean that several of them get weaker, since having too many of them available would be overpowered.
Vengeance could be a decent way to handle increasing threat generation for tanks, compared to some of the clunky mechanics we have now.
Ok, what about the other changes?
Rune system changes: meh. I guess we'll have to wait and see. Yes, we have tended to be fairly gcd-bound, pressing keys constantly, so if this change allows us to function with similar mechanics yet be more 'choosy' about the when and where of using abilities, it could be a good thing. I'll reserve judgement.
Outbreak: I like it, but I don't think it offers much. It's kind of a glyph of disease but for openers. I guess it will be nice to be able to apply diseases a little quicker.
Necrotic Strike: Bleh. How is this different from Death Strike again? It's a hot instead of instant heal? I dunno, sounds really boring, and redundant.
Dark Simulacrum: half a thumb up? Could be kind of fun, depending on how it works. It's not clear from the description if the target has to be targetting you, or if the attack is wasted if the incoming spell isn't 'reflectable.' It does just sound like a weak spell reflection (since it doesn't cancel the incoming spell).
I do like change to passive bonuses in trees in general: speccing the majority of our points in a tree get us that 'tree buff,' so unholy and frost dks get damage buffs (this isn't new, but still worth mentioning). It rewards you for committing to the tree that suits your style the most.
It will be interesting to see what they do with presences.
All in all, though, most of this doesn't do much to excite me. I'm hopeful they come up with better as we prepare for the journey to level 85 and beyond.