You have to differentiate being a hardcore gamer and being an addict gamer. I'm going to go out on a limb and assume that the majority of the readers of this site are hardcore gamers. We can play new games or old favorites for hours on end without negative consequences. An addict player plays games to a degree where it may have negative consequences to one's life. Compelling MMO's tend to be more addictive then other games. Just set your boundaries and you'll be fine.

I can admit that I was addicted to World of Warcraft for about 2 years. I played the game to cope during a transitional period in my life. When I first started playing, I just quit using drugs and I got out of a tumultuous relationship. I quit my job bartending at a strip club (where I met my ex) and got a 9-5. I used the game to substitute for everything I gave up. At first, I justified my playing the game so much because I thought, surely there are worst things. However, I gave up new and old social obligations because of it. I have a new job and a new significant other since I started, and I was still playing it. I had to take a few steps back and really look at where that time went. I did "meet" some really cool folks playing that game, but that game was becoming my 2nd life. I quit cold turkey about 2 months ago. I still have time left on my account, but I'm most likely not going back. I've been gaming since I was 5. I'm 26 now, but no game has ever consumed me like WoW. I'll stick to the occasional Team Fortress 2 and L4D for now. That way I can still enjoy life.