Warhammer 40K: Dawn of War: Soulstorm introduces two new races to the already overcrowded roster of seven races. Although one of the weaker races in the game, the Dark Eldar are built for speedy, run n' gun attacks. They also possess special abilities that can affect the entire battlefield, such as Screams of the Damned, which lowers morale. The new abilities are fueled by a new resource, soul essence. Although another resource may sound like an unnecessary headache, it doesn't alter gameplay in any significant way. Essence isn't hard to come by and there are even a few tricks that can be used to ensure a constant supply.
The Sisters of Battle are an all-female version of the Space Marines who help fill the Warhammer Universe's militant, religious zealot quota. The Sisters' strength is their infantry units, which can be upgraded with weapons that can quickly wear down vehicles and buildings over time and healing abilities. Similar to the Dark Eldar, the Sisters' also introduce a new resource, faith, which grants access to more powerful units, such as the aforementioned angel.
The remaining seven races also receive a few tweaks to help balance the game out. The most notable of the additions are air units, which are a first for the series. Air units act just like ground units and aren't integrated into the game all that well. Their only advantage is the ability to travel over any type of terrain, but they are easily shot down - making them more useful for quick strikes or as support for more powerful ground units.
As far as expansions go, Soulstorm feels more like a great series sendoff for fans rather than something that will pull new fans into the game. Though the gameplay might feel a little stale and doesn't quite stand up to recent genre entries, Soulstorm should delight long time fans looking for a new reason to jump back into the Warhammer universe.