Each player has two particularly-important statistics: “Satisfaction” (currently incorrectly labelled as “Happiness” in the player info window), and “Addiction”. Both these values currently range from -10 to +5.
Satisfaction goes up when good things happen (win a fight, have a good social experience, complete a quest, buy something valuable at a really good price, etc), and down when bad things happen (lose a fight, get affected by a bug, get banned, etc).
Addiction goes up and down based on certain sets of conditions. If good and bad things are both happening to the player for a long stretch of time, and the player’s satisfaction level is still positive, then addiction slowly goes up. If only good things or only bad things are occurring, then their addiction level slowly goes down.
When a player logs off, they might make a post online talking about your game (this is more likely as they become more addicted, and much more likely if they’re really unhappy with the game). Note that the further their satisfaction level is from zero, the more likely they are to make a post. If they do post, they’ll write a positive post if their satisfaction level is positive, or a negative one if their satisfaction level is negative.
source: Positive buzz and negative buzz