The Fallen Dynasty is the third adventure pack. It introduced new areas, new items, new monsters and quest lines. It added new content for characters levels 55 through 70:

Seven areas to explore
New solo and small group quests lines, as well as heroic and epic encounters for levels 55 through 70.
Brand new collection and tome quests
new artisan rewards that assist in the crafting process
Many new items, including weapons designed in the Fallen Dynasty theme