When last I wrote, my Death Knight was only level 74. This last Saturday I finally hit 80 and have come to some firm conclusions about the class in general. I definatly like the Blood tree the best, and like the Unholy tree the least. Well, perhaps that goes a little too far. Instead, let me say that I like the unholy attack rotations the least. There are too many interruptions (white hits) in the rotations because of cooldowns compared to blood rotations. And I generally just do not like that.
For blood I use IT > PS > HS > HS > OB > DC. For Unholy I would either use IT > PS > SS > BS > OB > DC or IT > PS > BS > BS > OB > DC. The IT > SS > BS > OB > DC rotation, however, introduces several second delays in the second rotation. And that equates to lower DPS which I do not like. Perhaps haste is the answer to that question, but I'm not a great fan of haste for Death Knights. I definately see it as a tertiary stat consideration when compared to raw attack power, strength, stamina, and crit.
By comparison you can use the blood rotation (IT > PS > HS > HS > OB > DC) on multi-rotation mobs with no delay. On multi-mob pulls you'd want to add in pestilence to the mix, so IT > PS > Pest > HS > HS > OB > DC.
I've been testing out several builds since the weekend, including various Unholy builds, but hadn't found one that offers what I see as acceptable health regen compared to blood either. Part of that problem, I know, is my low hit rating which I definitely need to raise before getting into anything really serious. I know this because I've been toying around with soloing Onyxia and I can see I miss entirely too many Death Strikes. I actually do much better as blood against her than I do as unholy. And in both cases I fight in frost presence, in tank gear (475 def, so still somewhat shy of the cap).
I've also been PVPing and definitely need to improve my skills before I start venturing into the arena. Part of my problem is I'm a semi-clicker. I use the default UI with some mods. So I'm limited to what I can put on the first bar. I have most of my key skills on the first bar, but some other important skills are on the top left and right bar which I have to click on. I could improve the situation by making some key bindings. And I'll most likely go ahead and do that. But I'm still a "clicker" by nature and move forward with the W key, and steer with my mouse. So any use of key bindings will require me to move my hand from the mouse to keys. With the skills on the first bar I generally use my left hand to click those.
PVP as a Death Knight is not nearly so easy as I would have assumed at first. It's a very busy class, and I find myself constantly looking down at my bars watching cool downs instead of keeping my eye on my opponent. So I'm going to have to look for mods that assist me with tracking cool downs.
In PVE I find that short of a Retribution Paladin, the Death Knight is perhaps the best soloing and farming class out there. I've literally played every class in WoW, with the sole exception of a Priest into end-game, so I have some perspective when comparing one with another. The Death Knight class has zero downtime. Warlock in a drain mode is probably very close, but I never killed things nearly so fast on my Lock as I do on my Death Knight.
Which of course leads directly into the greater conversation regarding how over powered Death Knights are. I still think that Death Knights are no more "over powered" that Retribution Paladins are. And while a very strong class, they definitely have their limitations. Kiting is still a problem, even with Death Grip. Mages are perhaps my biggest problem because Death Grip and root does nothing to them. They simply blink away, root me, then nuke me from afar. As blood you generally only have the AMS, which of course has a hefty cool down. And of course a Death Knight has to do damage to heal. No bubble/heal combo for them.