I enjoy this essay on MUDs and it seems to fit very well for MMOs as well. Now obviously, most of us would have aspects of all 4 player types, but which do you think you fit into most?
http://mud.co.uk/richard/hcds.htm
Player types:
• Socializer
• KillerSocialising with others.
Players use the game's communicative facilities, and apply the role-playing that these engender, as a context in which to converse (and otherwise interact) with their fellow players.
• AchieverImposition upon others.
Players use the tools provided by the game to cause distress to (or, in rare circumstances, to help) other players. Where permitted, this usually involves acquiring some weapon and applying it enthusiastically to the persona of another player in the game world.
• ExplorerAchievement within the game context.
Players give themselves game-related goals, and vigorously set out to achieve them. This usually means accumulating and disposing of large quantities of high-value treasure, or cutting a swathe through hordes of mobiles (ie. monsters built in to the virtual world).
Exploration of the game.
Players try to find out as much as they can about the virtual world. Although initially this means mapping its topology (ie. exploring the MUD's breadth), later it advances to experimentation with its physics (ie. exploring the MUD's depth).