Blizzard announced that there will be prologue missions released before Legacy of the Void to help connect the campaign to Heart of the Swarm. The way I interpret it the misisons will be free to all before the game is released, but if you preorder you get them even earlier. Not sure I'm reading that correctly. Maybe it's only available to people who preorder. Regardless I'm preordering for sure. So, this is awesome news IMO.