In my view, this is a difficult topic and made more difficult by unnecessarily bringing in language associated with destructive behaviour and physiological dependence. Certainly problems arise with playing too much. But most of the time, it isn't "addiction."
Engaging Is Different Than Addictive
First, it is very important to distinguish between "compelling" or "engaging" on the one hand, and "addictive" on the other. Using a term like addiction should not be done lightly as it runs the risk of—on the one hand—diminishing our understanding of real addictions and—on the other hand—possibly exaggerating what is merely compelling.
Keep Some Perspective
Second, it is important to keep some perspective. Often the times spent in an online pursuit are not more or less than would be spent by someone who is very committed to skiing, or golf, or swimming. We tend to gloss over the hours and hours that someone might spend perfecting their piano skills or their backflip into the water, because we associate those things with an approved and familiar activity.
Games Aren’t Socially Acceptable (Yet)
Third, are we talking about "addiction" because games are not (yet) socially acceptable, like golf, or chess or financially lucrative, like hockey or football or basketball? Many sports have prizes or fans or professional versions that further justify the time spent. Online games are (so far) not recognized in that way, although this is changing with the growing profile of eSports, for example.
The Benefits of Online Games Aren’t Recognized
Fourth, the benefits of sports or reading are "obvious" to us (fitness, and learning), while the advantages of online games—while they exist—are not as widely known or recognized. As a result we tend to lump video games in with harmful activities like drug taking. Although it is long forgotten now, "novel reading" was widely decried in the 1800s as a crazy pastime that was going to ruin youth, and women. The benefits of video games (some studies show educational benefits, decision-making benefits, team management and leadership benefits, etc) are still either not widely known or accepted. Perhaps, someday, we will have "xBox moms" (and dads) proudly driving their kids to practices in the minivan.
"Addiction" Takes Away Element of Choice
Another concern one might have about taking a behavioural issue, like playing video games, and lumping it in with physiological ones, like addiction, is that it removes the element of choice and responsibility from both the player and the player's family. Perhaps someone is playing a lot of video games for other reasons—loneliness, or physical disability, or who knows what. By making it "an addiction" then you take the focus away from the person and put it onto the game ("that game is SO addictive, they couldn't help themself").
I don't mean to suggest that there isn't a tendency among game companies to make their games as compelling as possible, to entice people to play and keep playing. Nor do I doubt that there are some people who become genuinely dependent. But, like Richard Wood, I think most of the time we are talking about "compelling" games and "engaged" players, not "addiction".
In terms of managing your time, I would suggest that players consider whether or not the game is keeping them from accomplishing other, important, goals in their life. If so, perhaps it is time to scale back the amount of time they are spending in the game. Parents might want to consider whether or not a child, for example, is even at an age where they can make those kinds of decisions. If not, then make the decision for them (plenty of tools exist, such as parental controls in the software, or just family rules).
Jackson, Leah. The rise of eSports in America. IGN. 25 July 2013. Available at http://ca.ign.com/articles/2013/07/25/the-rise-of-esports-in-america
Vogorinčić, Ana. "Panika oko čitanja romana u 18 st. u Engleskoj: Prikaz rane moralne medijske panike." Medijska istraživanja 14.2 (2008): 103-124. (English version here: http://hrcak.srce.hr/file/49661).
Wood, Richard TA. "Problems with the concept of video game 'addiction': Some case study examples." International Journal of Mental Health and Addiction 6.2 (2008): 169-178. http://laurier.communicationstudies.ca/files/wood_problems_game_addiction.pdf