The Diablo 4 open world is a real change for the franchise. We’ve always followed a path on the first playthrough that was impossible to deviate from. Diablo 4’s approach is quite different.
In Diablo 4 players will have a story to follow but it’s going to be up to the player to decide when to do what when they arrive in Sanctuary. You can of course roam around but players will always be led back to the story branches depending on how they approach the game. Acts can be tackled in different orders which is especially beneficial if you are on another playthrough.
There have been many comments about how empty the world feels and Blizzard has been trying to find a balance between having too much leaping out at you and not enough. I have no doubt this will continue to be tuned over the next beta phase.
Joe and Rod explain how this all works in the latest IGN video.