What makes a VTT work is that it is a sophisticated whiteboard application combined with RPG utilities (Dice roller, character sheets, etc) with voice/chat. The whiteboard aspect means all you need to do something is to be able to create or scan in a image, something that many of use already do in our regular tabletop game. Some things are easier like fog of war, and secret notes. Some things are harder, opening ports, everybody needing a copy, need to scan anything you want to show. But overall it is a win for tabletop roleplaying because gamers are doing same things and using the same products as they do in a regular tabletop game.
Ryan Dancey makes the following comment.
The problem is that VTTs exist, and they’re not successful. If you give people the choice between a VTT and an MMO, they pick the MMO. The VTT doesn’t solve the real problem that is that the MMO experience is simply better for a significant portion of the former TRPG social network. My opinion is that a successful and widely used VTT will remain an elusive mirage despite how much effort is poured into developing them.
Trying to compare VTTs with MMOs is indicative of a common problem in the industry in comparing tabletop roleplaying to other types of roleplaying games. The issue arises from the fact that myriad children of D&D compete and supplanttabletop roleplaying for many. Many in the industry, including Ryan Dancey look at these other forms of roleplaying and say to themselves "If we can take X feature from them, tabletop can now successfully compete."
Also Ryan and others propose creating games that fundamentally change the mechanics of tabletop RPGs in order to compete. Like eliminating the need for a human referee, zero prep games, collaborative story telling. They may create fun games as a result, but also games that are no longer tabletop roleplaying.
If tabletop roleplaying is to compete then it needs to emphasis the elements that are unique to it alone. Namely the human referee and how easy it is to let the imagination roam free with the human referee interacting with his players. Just as important making it easy for players to find one another.
Because of this VTTs are going to be an important element of tabletop roleplaying future. The whiteboard nature of the software makes it easy for the referee and the players to throw up whatever their imagination think of. Far easier than having to construct or place 3D objects and paint them with textures. All one has to do see this in action is look at the volume of fan fiction. It is far easier to write about your favorite things than to construct a 3D world, or shoot a video.
One thing that VTTs haven't effectively addressed yet is getting gamers together to game. Many are working on this including Wizards. What is needed is a site where hundreds or even thousands of gamers can browse to find open campaigns or create new campaigns. I personally think it will take a large preexisting network to make this happen. Either Facebook/Google+ will get a VTT app, or Paizo or Wizards throw their weight and resources behind one. Wizards has taken the first steps in this regard but not there yet.
VTTs are not the only answer. Things like an effective intro product, quality products, and game store events need to be part of the mix as well.