World of Warcraft - Learning From Past Releases has posted an article that examines some of the content and features included in World of Warcraft: The Burning Crusade, and then proceeds to suggest how Blizzard can build upon them in World of Warcraft: Wrath of the Lich King.
Blizzard has been quoted saying that they are happy with how Auchindoun Spirit Towers and Halaa in Nagrand worked. Having PvP areas within a zone that benefit everybody for that particular faction worked really well. Realising the positive effect of such areas prompted adding an entire non instanced PvP zone, Lake Wintersgrasp in WOTLK. The new zone features siege warfare and destructible buildings, meaning players can enjoy a much more engrossing PvP atmosphere. That's quite a step up from controlling a couple of towers. Hopefully further down the line, we will start to see more risk in PvP rather than simply a ghost or a lost objective.

Caverns of Time was a big success in the (what worked) department for Blizzard. Trapping various events in time forever is a great way to explain how past story lines come together to have effect in the current world. With WOTLK, the story of Arthas is retold in (The culling) using Stratholme as an additional (captured in time) dungeon. Using this way of telling stories from the past, players will find out just exactly what happened to Stratholme to turn it into such a forlorn place.