With MMO's, it is the genre that gets you interested, but it is the variety of things to do that keeps you there. This idea seems to be fading away as multiple events ingame seem to drive players in a certain directions, while the open-world aspect is relegated to grinding ad-nauseum to level up. A great MMO lets every aspect of the world contribute to the advancement of your player to the point where you don't even realize you are leveling up. Every corner of an MMO needs to be interesting to play either as a group or as an individual. You have to create a world where 200,000 or more people are going to log in everyday and find something interesting to do and something new to experience. The name of the game in MMO's is still addiction, how to get the player hooked on playing and keep them hooked on a regular basis? Repetition and "check-boxing" is not real addiction, curiosity is. A sense of curious wonder has to cultivated in the player with each login giving the player a vested interest in what is going on in the world you have created for them. A lot of F2P games seem to have replace this notion with access to loot for a price, playing to the lowest common denominator of MMOs, that being the hoarding of stuff. Ask yourself if the next MMO you play is grabbing your imagination or your greed?