Many of my friends refuse to play World of Warcraft because they're afraid of getting "addicted".  Players commonly refer to it as warcrack.  Probably a majority of the players regularly spend 3-4 hour long blocks on the game.  And so I've been wondering:  1) Why are MMORPGs so much more "addictive" than even the best of normal games?, and 2) Is there anything about World of Warcraft that makes it fundamentally different from earlier MMORPGs?
    In response to question 1, I have several thoughts.  Now, of course, many gamers right now are thinking, "Hey, WoW is certainly not the only game that people play for long amounts of time.  A lot of serious gamers don't even play mmorpgs!".  And of course they are right.  Most serious gamers have played a shooter, sim, platformer, etc., that was played for such length and intensity as to match the fervor of many wow players.  So certainly, this is not an original or unique phenomenon.  However, I think it would be harder to argue that any other game has illicited such common and widespread "addiction".  So why are mmorpgs, more so than other games, likely to get a player hooked?  I have thought of several reasons.
    1. Clear Goals and Rewards.  This is the most important factor early in the game.  The quests in World of Warcraft are generally fairly simple, progress is easily measured, and the rewards are listed and attained as soon as the goal is reached.  This cycle of instant gratification (quest-reward, quest-reward, and so on) essentially defines the majority of the game.  This creates an effect that could be called hypnotic, so that few people will actually realize how repetitive this is while playing it.  Even still, if all the quests were the same, this would get tiring quickly; but for the most part, the quests in WoW are varied enough.  Situations are different enough that there is a need to analyze, but not so different that the analysis is difficult or unintuitive.  Altogether, this creates a game pace that is constant but varied action; not so repetitive that one starts to notice the deficit of innovation, but repetitive enough, so that very little time is wasted trying to figure out how to do something.
    2.  Advancement.  This is kind of similar to the first.  The continual improvement of stats, armor, abilities, etc. can also create a hypnotic effect.  Obviously, this is not a concept peculiar to mmorpgs.  However, the social part of the game heightens these feelings.  Seeing more advance players creates a longing to attain that level of power;  playing with equals makes one feel satisfied and glad they have taken the time to attain this level, and looking on lower players creates a feeling of superiority and distinction.  This creates a powerful desire in the player to move up, and creates a constant striving for higher levels of power in alternation with satisfaction at how much the player has already attained.
    3.  Social Interaction.  Ultimately, this is of course the major distinction.  Any game can incorporate the first 2 aspects; this 3rd is largely peculiar to mmos.  In the beginning of the game, social interaction provides the variation and innovation that the game often lacks.  Now I'm guessing you yourself can imagine all the ways social interaction can vary gameplay, so I'm not going to go through that.  I do wish to talk about social interaction's role in end-game.
     When one looks at it, WoW is essentially two games, each of which is radically different.  The first is the leveling game, in which the first aspect i described is the major motivator.  End game, however, is completely reliant on social relations, and not simply for the reason that "it takes more than one person".  Social interaction is necessary for two reasons:
a.  More analysis is required.  Raid bosses do have a variation in abilities and strategies needed that is too great for simple intuition.  This would be intensely difficult and probably frustrating for an individual, but in a functioning group, it creates an immense sense of satisfaction.  Not only is the player working to achieve something that has more worth because it's difficult, they are also experiencing a greater degree of innovation and variation (because of the group) than was possible in the first game.
b.  The cycle of "quest-reward" has largely been broken.  Neither the completion of the quest nor the existence of a reward can be guarenteed.  The group dynamic is thus necessary to replace this.  It does this in three ways:
  1.  The group becomes a force in its own right, dedicated to advancement.  Thus the group can exert a pressure on individuals, either through persuasion or coercion, to continue playing.
   2.  Normal social interaction.  Guilds often become, essentially, chat rooms, and this interaction with others helps to alleviate some of the boredome during raids and friendships are a motivating force to continue playing.
   3.  The promise of rewards.  Rewards are not guaranteed or instant, but as long as the group maintains steady progress, this only makes the desire for these rewards more intense.  The effect is not hypnotic, but it is probably more addictive because there is more of an emphasis on the goal than on the gameplay.

I will attempt to answer the second question later...