I don't even have a Facebook account, and Farmville doesn't look fun.
It's eye candy. The farms are pretty and we (used to) build them based on our own personal likes and dislikes. And the up-leveling gives a feeling of accomplishment not based in reality, same as with any such game.
"I absorb energy like a sponge everywhere I go. It allows me to see the world and my purpose in it." Zak Bagans, Ghost Adventures (INFJ)