Breadth and depth of narratives in games- Games are said to have little breadth as the goal is usually simply to win and nothing more. However games can have varying degrees of depth (complexity) strategy games such as chess have depth as players can use complex strategy against their opponant in order to win. On the other hand a simple game of snap has little depth as the strategy is little more then luck and quick reflex action.
Richard Bartles artical on MUDS (Multi-user Dungeons). Multi-user refers to one world (virtual computer generated map) being shared by many online users. Multi user dungeon games combine the features of an RPG, multiplayer interactive, combat, and online social chat. This link takes you to a full artical
Richard Bartle has identified 4 main processes of exploration a gamer goes through.

1. Goals and Targets - Players usually start a game by establishing a target or goal to achieve.
2. Exploring the map- Initially players explore the scenery (Bartle refers to players exploring its breadth) but later progresses to the exploration of the games physics engine (games depth)
3. Socialising with others.
4. Using tools to impose distress
Massive multiplayer online Games (MMOG) involve a significantly large online community where thousands of players join servers and play games together. Interaction between players plays a significant part in making the gaming experience enjoyable and addictive perhaps more so then playing the game itself. The core story of a multiplayer game is never resolved, and some debate whether this type of social interaction should even be referred to as a game.
Massive multiplayer role playing games (MMORPG) such as World of Warcraft involves an imperfective storyline approach, whereby a player (to some extent) makes the desicions of how the story panns out and what kind of a role their character plays. The offline RPG game involves alot more choice and desicion making giving the gamer more freedom

Similar to the MMOG- Social Networking virtual worlds.
These games have no narrative at all, no combat, and no statistics to improve but they do have an economy. This kind of gaming is purely social, you can customise your avatar and various other elements as you like.
MMORPG'S structure of a game