Bizzard has a new article talking about the new adventure mode that you can choose to play in Diablo III: Reaper of Souls.
More information.Introducing: Adventure Mode
In Diablo® III's upcoming expansion, Reaper of Souls™, players will have the opportunity to choose between two different modes whenever creating a new game: Campaign Mode and Adventure Mode.
Campaign Mode
In Campaign Mode, players reprise their pivotal roles as the heroes of Sanctuary. With a greater focus on story, all of the quests, cut-scenes, and in-game movies will remain available to you in this mode. Progression through the game's five thrilling Acts is intentionally linear. Campaign Mode is very similar to the current Diablo III experience.
Adventure Mode
In Adventure Mode, the majority of these story-driven elements have been removed and all waypoints have been unlocked, allowing players the freedom to explore and play the game however they like—even across all Acts. The world itself is your battlefield. Go anywhere, slay anything!
These modes can be accessed at any time, and you're welcome to switch between them whenever you please. In addition, we've unlocked all difficulty levels, giving you even more control over your in-game experience. Don't want to play through the story four times on each of your characters? Done. Looking to farm in Adventure Mode at one difficulty, then switch over to Campaign Mode at a different difficulty? You've got it.