It all began with LAN based games that involved the building of a village or kingdom. Games like Age of Empires, Zeus and World of Warcraft etc. may be called the predecessors of online games such as Farmville. While these games consisted of building kingdoms and the romanticism of playing as historical characters, Farmville is more escapist in nature.
Online games like Farmville are a sign of growing escapism
The online gaming audience is now looking for something new to take onboard. This is the chief reason for the success of online games like Farmville, which is a different offering.
Online games give one a shared sense of community
Many also subscribe to the fact that given the explosion of online media, you know people are more likely to meet you online than in person. This in turn has created the latent need for a growing sense of community. While there are games online that are popular such as Crazy Taxi and Tower Blocks, they do not give one the large number of options Farmville gives.
A similar online game that had a short run was Mafia Wars. This game again emphasised the concept of mafia families in gameplay parlance. Again this was an indication of a shared sense of community for people who might not talk to each other in person, but trade together on the online gaming front.