For single-player games, branching open-layout dungeons are great. However, unless they are procedurally generated (I.e. PotD or HoH), they are pointless in repeatable group content, especially if the group is auto-matched. For the first day or so after release, people might explore but the community will very quickly settle on a standard path that everyone is pressured to stick to, and deviating from that path will get you labeled as "bad".