With each patch and expansion, Blizzard has demonstrated a keen sense of learning. One of the things I truly enjoy about their talks, such as the panels during the Worldwide Invitational event in Paris, France last month, is when they illustrate their learnings and what they've come up with in response. For the most part, each iteration of their designs is progressively better than the last. Take World PvP, for example. Their first attempts were silly and laughable, such as the sandlol in Silithus. In Outlands, however, they implemented several World PvP objectives that were more successful, particularly Halaa and the Bone Wastes. In Blizzcon 2007, they talked about the things they learned so far, which make me truly excited for Lake Wintergrasp.
The Death Knight is another matter altogether. It's a new class. With the Burning Crusade, Blizzard simply added new races, which wasn't too difficult to balance. With the coming expansion, they've designed a class from the ground up -- and from what I can see so far, they've broken the mold and created something that doesn't quite follow the conventions we're become accustomed to. If anything, the Death Knight is a shock to the system. Looking through the talents and spells, a few key design points stood out for me.