I have an addictive personality--I am also highly competitive. This is a dynamite and dangerous combination when it comes to games in which you pit yourself against opponents, obstacles, or both. When the opponents are not computer generated, there is also a sense of community that springs up among people on one 'side' vs. the other 'side'.
You may maintain your "I"ness, your persona, but it gets subverted into a kind of group mode in order to succeed in quests, adventures, or goals that are group oriented. The "I" is there, but it's now involved in making decisions that affect the entire group, and the more independent you are, it is both harder and easier at the same time to devote your energies to that group and that goal.
I have just finished a year long stint with a game called RailNation. There were four separate games played, each lasting 12 weeks, with a slight space between each one. It was played out on a map of the United States, and you settled (with your association) in one city and 'owned' it. It is, frankly, maddeningly, one of the best, hardest, and most interesting games I have ever played, one of the most addictive, and it required attention on a daily/hourly basis. Unlike many games, WoW most notably, it continued on whether you were logged on or not. That meant you were more or less forced to show up fairly regularly in order to be productive and useful to your Association.
I loved it, and hated it by the end of the last round, which ended last week.
I'm gone. The new game started today, I went over and saw that I could log in, and I fled. Seriously. Took down the shortcut and the references to it.
Then I went out and mowed the lawn.