The big problem is non-linear dungeons do not work well in a random match making system. When you throw 4 random people together and have choices then you will have issues where player A wants to clear the whole place but player B only wants to kill the end boss and get out. I saw this a lot in WoW with the few dungeons that had optional bosses. If that optional boss did not drop something the tank wanted good luck getting them to go that way for your potential drop, etc.