Second Life is not what it might become, not yet. Right now, like all new media and new forms, it is drawing heavily from previous forms, some very recent, some much older. It draws from the chat rooms and fan communities of the early Net. It draws from film, and video games. It draws from the pre-Enclosure experience of "the commons," where a natural park-like area was left in the middle of the town or village, owned by no one, maintained in common, where everyone could graze their cattle, wander about, and meet others in unscripted and spontaneous ways.
But SL is not yet greater than the sum of these parts; right now it is actually smaller. Its art and social forms are derivative, as is natural at first. It is a less compelling film experience than film, a less compelling game experience than the current sophisticated video games, a less compelling social experience than hanging out in RL, less compelling than the actual experience of Burning Man (the communal creative chaos of which inspired it), and, even less compelling than text-based chatting like IM, which contains pauses and non-visual components that allow for composition and narrative shaping to a much greater degree than 3D meetings, which offer "too much information" to make good stories.
Where virtual worlds might be going is not yet determined, but it will not be determined by interaction on their most superficial top level, inhabiting the world as an avatar, nor on their next level down, building and scripting using the in-world tools.
The new meaning of virtual worlds will be determined by something much deeper, by a creativity constructed by and embedded in its application code and hardware composition. The visual and social forms that will appear on top of those layers will have the potential to be new in interesting ways, because the theory and structure that underlie them will be new in interesting ways. At that point the graphics may still be simplistic and the interaction laggy, and the form may take awhile to catch up and elaborate on the structure, but it will be going in a new direction and inhabiting a new conceptual landscape, and so will we. That is the potential of this new media, and that is what will be worth experiencing.