All games are better when played with people you know, but MMOs live and die by my ability to play with people who don’t suck. (not just suck at the game but don’t suck at being people) WoW is crazy successful not really through any bit of design or some ground breaking game play but because it percolated for so long as the only arcade style MMO and made it easy for the massive community that exists now to germinate and maintain. In fact I would say that the community is keeping itself and WoW alive now long past the quality peak of the game. Jeff hit it on the head when he said that Blizzard doesn't know why WoW is successful. They keep focusing on changing the mechanics more then actual player experience when the real amazing advances they have made are their group finder and raid finder tech. The tweets from their design staff seem so confused over trying to manage player reaction to their content, then just making sure players just have access to that content.
New MMOs have such a huge focus on world and mechanic design and very rarely engage the community they are going to need when constructing their game. The big sin that SWTOR made was doing a great job of engagement with their community in the beginning and then completely ignoring them after launch.
The biggest reason that F2P is great for MMOs now is that it gives them the ability to exist for a while in near profitability while they build that community they need to survive. Then once that community arises the micro transaction economy is a direct pipeline into that community to deliver content that is laser focused on their desires and priced according to that demand. Another SWTOR sin in that all their micro transaction offerings have been more about Star Wars then about the needs and desires of the player base.