There are more subtle ways of gaming ruining your life, as well: slowly losing the drive to do anything more than what's necessary to pay the cable bill, rent, and the gaming subscription. Slowly the only friends you have are people you know from your guild. When the only source & output of creativity and energy are all wrapped up in playing a video game. I've also seen people similarly consumed by pornography, alcoh…
Most of my friends consisted of people whom I gamed with -- I barely made any friends in college. And of course, most of those gaming friendships never developed into any sort of deeper connection. Having made friends "IRL" with whom I have deeper connections than playing video games, I can't tell you how much more enriching that is.
Also, I now have all sorts of interests that require lots of something that I once had but now don't: time. In college, I now understand, I had so much time with which to learn and create. Instead I squandered it all away. I did graduate cum laude, so it's not like I was a total slacker, but I could have spent my time in ways that would have been far more interesting and rewarding than clicking, clicking...
Furthermore, I now have problems with my left hand as a result of holding down WASD so much. That's not something that can necessarily ever be fixed, which is frustrating to me as someone who once played musical instruments. I gave up being able to play guitar and violin for what? For video games?
Yes, I have Diablo 3 and I see that many of my friends are on Hell difficulty now and level 55 or whatever. They did that in 2 or 3 days while I still haven't beaten normal mode. And even though I'm having a bit of fun playing Diablo 3, it can never compare to the enjoyment that I once had playing instruments. And what's sad is that _I knew this_ at the time, but it was so much _easier_ to play games than to do any of these other more rewarding but more challenging activities.
Was I addicted to video games? I don't think I've suffered from any of the more classical addictions like alcoholism, so I can't fully compare. But in retrospect, I think that I was. I was always interested in games as a kid (playing NES), but I think that I really turned to games after a particularly traumatic event in my life. From that point on, gaming became an outlet for psychological stress and personal insecurities. And as time went on with me using gaming as a bad coping mechanism, additional negative effects accrued: for instance, I lost that drive in life which boredguy8 mentioned.
Well, I'm rambling a bit now... but what I wanted to convey was that if you find that what I said about my relationship with gaming resonates with you, please take some time to reflect upon yourself and the way in which you are using the gift that is your unrepeatable life. Examine yourself and see if there are perhaps deeper problems with which you need to get help, problems which are being masked by gaming. And if you can't figure this out through self-examination, please find someone who can help you. There's more to life than playing games.