Bioware is touting its entry into the MMO arena as one that doesn't sacrifice story in favor of grinding, looting, raiding, and levelling up. A good story has historically been very difficult to pull off in an MMO setting precisely because of the nature of MMO's. Persistent worlds require exactly that: persistence. However, persistence also makes telling a good story very, very difficult, as any good story always requires great change either personally for individual characters, or for the world as a whole, and oftentimes requires both.
Whether or not Bioware will be able to pull off a successful story through its next venture is yet to be seen, though the features they've implemented so far to support this claim do sound promising: voiced characters, dialogue choices, and multiple ways to resolve quests (light side or dark side).
Visit The Old Republic's website for more information or to catch the original three cinematic trailers, developed and animated by Blur studios. All three of them beat the prequel movies hands down.