I've now taken my DK into a couple of dungeons - one Heroic Bloodmaul Slag Mines (which gear trivialized) and one Timewalker Slave Pens.
Having Death Strike as our RP-spender really frees up Runes to do other things in the rotation. It's a change that, now that it's there, really does wonders for the rest of the rotation.
The real back-and-forth trade for Blood is going to be Marrowrend or Heart Strike. Marrowrend stacks up Bone Shield charges, which of course really improves your survivability, reducing damage taken by 20% and increasing haste by 10% while you have any charges (and with with the Ossuray talent, reducing the cost of Death Strike.)
Heart Strike, on the other hand, does way more damage-per-Rune and also generates 5 extra Runic Power. So two Heart Strikes costs the same number of Runes as a Marrowrend and generates 10 more Runic Power, which of course means more Death Strikes.
My general sense is that Marrowrend is better on single targets like bosses, because you're going to have fewer swings at you, and thus the Bone Shield buff will stay on longer. Trying to keep up Bone Shield when there's a large group of enemies - or even just four or five like a typical trash pack - is going to be very tough. So my impression (and remember, I'm not a real theorycrafter) is that you should stick to Heart Strike for the extra RP. Given that Death and Decay's cooldown gets reset and it becomes free thanks to Crimson Scourge pretty often, you'll also be doing a ton of damage with Heartstrike to these large groups, as D&D adds three targets to Heart Strike.
Damage and Threat:
You will have some downtime if you don't have tons of Haste. Blood no longer has any sort of Runic Power or Runic Corruption sort of passive, so when you spend your runes, you just have to wait (though Blood Tap is now a talent, which works a little differently but allows you to gain runes back on demand.)
Blood Boil is a fantastic group-pulling tool. You might use it rotationally as well, but I've been saving it for snap-threat. It applies Blood Plague, which heals you and of course deals a fair amount of damage over time. Thankfully your Crimson Scourge proc seems to happen pretty frequenly, and Gorefiend's Grasp is now baseline for the spec, letting you gather up groups with ease.
One ability I haven't quite figured out yet is Death's Caress, which is kind of an Icy Touch for Blood Plague. It does way less damage than Blood Boil and, unlike BB, which is free apart from its recharge, this costs a Rune. I do use it for pulling, but I suspect I shouldn't. I definitely think Blood Boil is better for refreshing the disease in the middle of longer fights. So... who knows?
While you do want to keep enemies in your Death and Decay, it's not as core to the rotation as, say, Consecration for Paladins is. Blood Boil should keep your enemies interested in you, and if you need to get somewhere far away fast, you have Wraith Walk, which gives you three seconds of 70% increased movement speed, though if you do anything during the Walk it will end.
Overall I think Blood is in a good place. With the paradigm of tanking shifting more into the "you will hover somewhere in the middle of your health pool" zone, Blood's self-healing really shines.