In my opinion, it's going to come down to technical issues.
The immediate success of the game is going to come down to whether or not the team can hammer down on the de-syncing I've been seeing as rather rampant in videos and streams, and complained about on various forums.
Everything else looks great! Solid core gameplay, good skill tree design, interesting premise and world, unique tie in element. Content can be pushed out over time and people also have the show and the story based events it will likely spawn in the world to keep them busy and happy.
As long as initial impressions aren't soured by instability, I think this game will speak for itself quite well and potentially go very far. Especially considering the theoretical sales on 3 major markets (PS3, Xbox AND pc).