The Dark Eldar and Sisters of Battle will offer up some interesting new approaches to the game. The former are an offshoot of the Eldar faction, though much more evil. The Dark Eldar is basically a pirate race that specializes in quick strikes, using speed and poison abilities to stun the enemy. Their units tend to be fairly mobile, such as the scourge, which are heavy infantry equipped with bat wings that let them jump and hover. On top of that, the Dark Eldar utilize a third resource that's unique to them: souls. The Dark Eldar consume souls, so when they kill an enemy they can collect the soul essence that is left behind. The Sisters of Battle, on the other hand, are basically heavily armed warrior nuns and the feared enforcers of the Imperium. As described to us, they're basically the Spanish Inquisition in space. The Sisters are driven by faith, which lets them call on their God-Emperor for "Acts of the Faith," which are powerful abilities, like a protective hand that shields them from damage or raining brimstone down on the battlefield. These acts are fueled by faith, which can be generated if the Sisters divert resources from unit production and research. That will make you have to choose how much to spend on the economy and how much to spend on generating faith.