The main new feature of the game are battles on sea. Each faction has access to different ships and even submarines. You can also hire mercenaries which help you to defeat your enemy in the new single-player campaign and on the 25 new multiplayer maps...but only if you pay enough of course.
There are also two new multiplayer modes: Marine One down and SCUD-Hunt.
In Marine One down it is your goal to get the president to the evacuation-zone. The last player who was near the president can control him.
Were in SCUD-Hunt you need to get your hands on a SCUD-thrower. If you posses it you have access to your super-weapons.
The add-on also features 50 new units and upgrades for all sides as well as better graphics, a better AI, new multiplayer options and several other minor changes.