Imperial Guard
A new faction was included, the Imperial Guard, with some units previously available in certain single player missions of Dawn of War.

The Imperial Guard specializes in defense and attrition warfare, and therefore has the strongest defensive structures of all the factions in the game, as well as garrisonable production structures and a tunnel network between them, allowing stealthy transfer of troops. Their infantry tends to be of lower quality than that of their opponents in terms of weapons, armor, and morale, due to Guardsmen being regular humans, but the Imperial Guard makes up for this with a range of powerful armoured vehicles, such as the Leman Russ and the Baneblade, as well as the Sentinel walkers, which until the Dark Crusade expansion were the only vehicular unit in the game which could uncapture strategic points. Also, uniquely, the Imperial Guard features not a single primary hero but a Command Squad staffed by a General and up to four secondary heroes, as well as up to 13 stand-alone secondary heroes, 8 out of which are Commissars or Priests that are much more effective when attached to squads (e.g. a Commissar solves all morale problems).

New Campaign[edit]
There are two new single player campaigns, both of which involve each faction attempting to recover a lost Imperator Class Imperial Titan. All races from Dawn of War (Orks, Eldar, Chaos, and Space Marines) are available in addition to the new Imperial Guard, with each race trying to find and gain control of the Titan for their own reasons. Although the Titan as a whole is not controllable, its weapon systems can be used to assist in the destruction of the Necrons, who make a cameo in the final mission for each faction. In this campaign at the beginning you have a choice to either go with disorder, who are Orks and Chaos, or with order which at the beginning is Eldar and Imperial Guard with the odd appearance of the Space Marines.

Other changes
Many of the units available in Dawn of War were simplified, reduced or limited for the Winter Assault expansion. For example, Space Marine Predator tanks were limited to carrying anti-tank weapons while Chaos Predators were limited to anti-personnel weapons. In the original Dawn of War game both sides could upgrade their tanks from anti-personnel to anti-tank (Destructor pattern and Annihilator pattern respectively). Likewise the Land Raider was limited to one per player but in turn had greatly increased durability.

Limitations were also applied to the Orks, who lost most of their upgrade choices and became limited in their weapon choices. The Eldar had their "hard counters" removed, meaning that specialized units such as Dark Reapers were no longer as prominently effective against heavy infantry. Some units, including most of the Ork army, also lost the ability to use grenades. The Chaos Space Marines also lost the ability to upgrade to any heavy weapons other than the heavy bolter and plasma gun.