Rueben Steiger, CEO of Virtual world ad agency specialist Millions of Us, gave a talk during GDC and Gamasutra had a recap. He says the reason that virtual worlds have had initial success is due to the lack of rules and openness, the user defines the fun, not a game designer. However, hybrids with more traditional game mechanics are “probably a lot more mass market friendly.”
I think he’s right, casual users will appreciate the openess that a virtual world can offer, but they want to be told what to do. They want goals and missions. They don’t want to always have to make their own fun. Second Life is a good example of being too open and not offering enough goal oriented content. SL has yet to reach mass market adoption and have even seen their growth plateau recently.