Lots of good points in this thread.
Surely, by its very essence, an adventure game is like a novel brought to the computer screen. It has a definite beginning and end. With a clear thread running between the two. And clearly delineated characters, a constant setting, etc.
What most people seem to describe when they talk about multiplayer adventure games are really not adventure games at all, but rather “life simulations” (for lack of a better word). You know, they are virtual worlds within which the player get to play out some fantasy life, facing the challenges that go with that life.
Anyway, I’m not saying it’s impossible to build a successful on-line adventure game. Merely that it would be difficult (and that the gameplay would necessitate certain restrictions that MMORPG players may find frustrating or annoying). All the same, it’s a project I would love to be a part of!