Hi everyone,
I'll post here the main changes the dk will be going through both for the raid leaders who'd like a quick review, and for whoever is planning to switch to a dk but isn't sure yet. For in depth analysis, i suggest you the elitistjerks forum (http://elitistjerks.com/f72/). Of course, if you would like to contribute to this thread by correcting/adding some information you feel has been overlooked, please do it! :D
Generally speaking, the feeling of a dk should not change, the rotations of the various spec should be pretty similar to the one used in cataclysm, with some rare exception and the introduction of soul reaper.
About raid utility, unholy will lose desecration, but the anti magic zone will be talented, meaning that any spec will be able to pick it up. As far as i've seen, the AoE slow wil be good on any spec, with the frost spec being the most reliable due to the low cooldown on howling blast. Some talents will be solid picks, and i was a bit surprised how useful many of them can be for a blood dk, like purgatory in combination with death pact, or conversion. Conversion, for example, is very much like enraged regeneration for druids and warriors, but it's not limited by a buff duration: the spell tooltip states clearly that it will last until cancelled or no rune power to feed it. This, in combination with the right choice of rune regeneration talent and a bit of luck on RNG, has very good potential, even tho Death Pact will usually be the talent picked since it will offer a generally better and more reliable heal.
For what concerns the dps specs, the talent will not offer great improvements in dps, but just raid utilities and bonus for the player, so pretty much take the one you feel it's more useful for your play style unless of course the raid needs a specific tool. There shouldn't be much difference in terms of dps output, however it's too early to say that and i've never tested the new specs and features so far, but i'm pretty sure that there will be a lot of balancing hotfixes in the worst cases.
Keep in mind that i've never tried out the new specs/talents, since i've never been in the beta testing and the patch goes live tomorrow, so these are just speculations based on the information retrieved online and my experience with the class.
P.S.: Just a personal note: unholy is very fun to play, but bugged fights like madness of deathwing in ds made it the most frustrating nightmare for me.