Vaneras posted a much-needed FAQ on the new Death Knight class that answers a few important questions about the nature of the class and how to achieve it:
There are a lot of things still being worked out with the Death Knight class such as specific spell abilities. Unlike a traditional caster type however, a Death Knight's spell power comes from runes that are etched into their blade. Think Warcraft III when you think about the possibilities of abilities for the Death Knight. I say possibilities because things are still in process for the development of the class and there will be (of course) a lot of testing for balance done. Given that this is our first Hero class we're unveiling, you can be sure we're going for the coolest of the cool for this class.
The post itself is simply a recapping of all the information heretofore known about the first hero class but hopefully it'll remind those who are already writing complaint posts on the forums that the class is still very much in design.
