But for anyone to become seriously negatively affected by a video game (or anything at all, except for say substances that have physiological affects on a person), I truly believe there has to be some underlying problem or flaw in the personality to begin with.
Right, and that's the way addiction always works. It's always the substance/process + the vulnerabilities of that person. It's not always simply "a flaw in the personality," though -- it can also relate to the culture (country, family) they are a part of, or their genetic heritage/vulnerability. But it certainly does have a lot to do with that person: their development, choices, unmet needs, unresolved issues (especially trauma), impulsivity, risk-taking ... just their overall psychology. Nothing is addictive in and of itself, not even heroin. It's always a combination of the substance/process plus the vulnerabilities of that particular person, in that particular environment.
Re. the hook or "high" of MMOs":
Well with DAOC, to me it was the competition. It was about having our guild be in the top 5 guilds as far as points and about me trying to be # 1 in my particular class/server. That certainly drove me to keep playing.
Also, the people were nice and we'd play using voice chat so some days there wouldn't be any playing really, just a bunch of us chatting and goofing off. So there was the social aspect.
But above all, it was just fun. ... It was a blast to storm an enemy tower in a group (of 8), kill it's guards and try to break down the gates with battering rams as quickly as possible before the real life players of that realm came to defend. Once we captured and defended a tower successfully, we'd move on the the next tower all the while putting the call to other guildies or realm mates to start taking other towers.
Sounds like the standard appeal of online gaming: competition, social chatter, and shared tasks/accomplishments. I'm afraid (or perhaps glad) that these things really don't appeal to me that much. I'm not a competitive guy. I'm an introvert so don't find social chatter entertaining. And I prefer working alone, since that gives me control over tasks, directions, choices, and pacing, whereas in co-op games, I always feel like my direction and pace is dictated by the group. Meh. I let my Xbox Live subscription expire a few days ago because after 6 years of trying to get myself to enjoy online gaming, I can't do it.