Ghostcrawler has realized that the Rune mechanics that are introduced in Cataclysm, is a bit confusing. So, neither short nor lazy, he has written one of his long posts to explain us and, with simple analogies, you may understand all this better.
In addition to this, a few more things have been added to the Advancement of the Death Knight in Cataclysm.
I'll explain the rune mechanics better. Once you see it in action it's pretty easy to understand.
Focus on the Blood Runes for now. The big change is that rune # 2 will never start to fill until rune # 1 is full. It will always fill 1 and then 2. Today 1 and 2 can be filled at the same time.
In Cataclysm, when you're killing things, you use rune 1. Then any extra "red" on rune 2 will fill rune 1 again. If both are full, you can use two blood runes immediately. But after that, rune 1 will fill up first and then rune 2. For if it helps, imagine that rune 2 is a secondary deposit.
It will sound to you as if we are slowing down CoM attacks and that is to some extent. It is part of what we are trying to achieve. We can supplement those skills that use the global cooldown with things like Free Skills or Runic Power skills, or maybe it gives us room to add talents that make runes refill faster. Remember, though, that slow attacks can hit harder. Instead of the Death Knights hitting fast like a Rogue, they will hit slower and harder, like a warrior. This is the image that many players have of the Death Knight. Double grip will hit faster of course.
I'll try another comparison. Imagine that all the rogue's abilities cost 100 energy. They would have to wait until they got 100 energy and then immediately use an attack so they weren't wasting future energy. This is how CoM works now, except they have 6 runes to watch out for. Now imagine the same rogue but all his abilities cost 50 energy. If he makes an attack when he has 60 energy, he consumes 50 but has 10 remaining for the next attack. This is how we want the CdlM to work.
If it still doesn't make sense to you, then focus on the experience that will be, that is, you will have more court to breathe in your rotation and you will not have to press buttons every Global Cooldown. If you don't use a hit in the second it's available, it's a bit better because the extra deposit will save extra resources instead of wasting them. However, you will still be pressing many buttons. We will keep the double runic strikes, Runes of Death and multiple diseases and all the fanfare. We have to make some changes to some skills to accommodate the changes in resources but it is not something that is unrecognizable.
We're not even sure the CoMs need Runic Strike anymore. If it survives, we will make it an instant hit. But if we make it an instant hit, it won't be that different from existing hits so we may be able to do a tank rotation without it.