As you can by the trailer, there will be three different races you can fight as: Space Marines, Orks, and Eldar. Missions will alternate between these groups as you play through the main campaign.
As clarified by PC Gamer, this third entry will combine the best of the first two games while including some new features of its own.
For the first time since the original, bases and giant armies are back. The bases produce many of your units such as Tactical Marines of Devastators. You can also load your lazy soldiers into a drop pod. These smash down from above, sometimes crushing the enemies. At any one time, dozens of units may be fighting each other. While this may seem hectic, the designers have made every aspect of battle easy to identify.If you’re as much of a fan of the Dawn of War 3 announcement trailer as we are, than you have to admit that the visualization of hundreds of discarded soldiers literally raining down is hard to beat. Keep checking back as more information is revealed.