Sweet Emperor's teeth, yes! The Sisters, even with their late 3rd Edition Codex, still lay a disproportionate amount of hurt down. They're arguably the best army in the game, and here's why.
Sisters are able to bring numbers to bear-- it's not hard to bring 100 Sisters in 2000 points and still have all the hardware you need besides. They have the same equipment (barring the bolt pistol and grenades that come standard in the new Space Marine codecies) as Space Marines, so at range, a Sister is identical to a Space Marine. Up close, Sisters can bring a disproportionate number of high-yield special weapons to bear, and combine close-range fire with Acts of Faith to leave nothing left standing. In close combat, Sisters may initially look like a weak army, but it's quite the opposite-- while they're T3 and WS3, a Sister has a 3+ armor save, and Acts of Faith can exponentially increase their damage output and survivability. Then, there's the Veteran Superior with the eviscerator... Think of it like this. The army's got the hitting power of an Eldar army built to be a short range powerhouse without the drawback of low numbers and average at best armor saves.
Sisters work best when you have several squads working together, rather than sending a single squad to go deal with a given threat as you might with a Space Marine army. Three squads of Sisters in Rhinos are a -huge- problem for an opponent, but ten Sisters on foot really isn't that big an issue. An armored thrust backed up by Immolators, Exorcists, and Seraphim makes sure that the threats to the Sisters of Battle squads that are mounted are neutralized, and the Rhino push is able to get in and burn the enemy battle line with heavy flamers and meltaguns.
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