Anarchy Online: In 'my' opinion the master MMORPG at this time is and has been Anarchy Online. Why do I say this? Because AO is the most complex, evolved and balanced of the genre. Many games have various features of note but AO brings together a complete package. It is also one of the lesser known of the genre partially because of the complexity. The main reason people try but don't stay is because of this feature. This also causes the average maturity and intellectual level of the players of the game to be much higher than others of the genre. This is not a boast. Something is to be said for simplicity in entertainment and relaxation which counters the very complexity of this game. Complexity also requires a certain dedication to the game to get a meaningful experience from it.

A good explanation of the game is at Wikipedia.