From the game's official website:
Command the seas, control the land, forge a new nation, and conquer the globe. Empire: Total War takes the Total War franchise to the eighteenth century Age of Enlightenment -- a time of political upheaval, military advancements, and radical thought, captured in stunning detail in Empire: Total War.
Empire: Total War introduces a host of revolutionary new features, including true 3D naval combat. For the first time in the Total War series, you will be able to intuitively command single ships or vast fleets upon seascapes rich with extraordinary water and weather effects that play a huge role in your eventual glorious success or ignominious defeat. After pummelling your enemy with cannon fire, close in to grapple their ship and prepare to board, taking control of your men as they fight hand-to-hand on the decks of these wooden behemoths.
In addition, Empire: Total War will see further enhancements to the Total War series’ signature 3D battles and turn-based campaign map. Real-time battles will pose new challenges with the addition of cannon and musket, challenging players to master new formations and tactics as a result of the increasing role of gunpowder within warfare. And the Campaign Map -- for many, the heart of Total War -- introduces a variety of new and upgraded elements, including new systems for Trade, Diplomacy and Espionage with agents; a refined and streamlined UI; improved Advisors; and a vastly extended scope, taking in the riches of India, the turbulence of Europe and, for the first time, the untapped potential of the United States of America.