"Anno 1701: The Sunken Dragon" includes new features, new missions, and a map editor.
It also contains some new player profiles. Profiles confirmed are:
Diego del Torro
Next to this some new ornamentals are available:
A Voliere/ Birdhouse
A Fence, covered with roses
The add-on has an Asiatic look, as well as a campaign with 11 missions centered around the new player profiles
Anno 1701 The Sunken Dragon, like the other four Anno games, is a game based mainly on the economics of the settlement created by the player. The more skilled a player is at maintaining a balanced economy the more successful their settlement will be.
Source: Wikipedia, "Anno 1701", available under the CC-BY-SA License.