I've watched this happen to my friends.
One that I graduated high school with in particular comes to mind. We all played video games back then. Half Life, Goldeneye, Starcraft, Everquest, etc. He was a smart guy, driven, usually made better grades than me (I was lazy in high school). Took a job at an medical supply company after graduating from high school intending to work for a few months before starting college.
Well, when it came time to start school, he tried to balance work, school and an ever increasing amount of time in front of the TV or computer playing games ... and failed. Dropped out of school after one semester. Got an apartment with a couple of his coworkers where they would mostly play games when they weren't working. I went over a few times. It was depressing to watch. You really want to say, "Dude, is this really what you want to do?"
Spent seven years working that same job stocking shelves and spent the rest of the time drinking and playing whatever the newest game was that month. He'd message me at like 12am asking if I was playing anything and I'd be like, nope, studying. He'd type "LOL" (back in the AIM days).
When World of Warcraft came out, he was instantly drawn into the WoW universe. He'd stay up all night playing. Broke up with his girlfriend because he was playing WoW literally every waking moment. Started being late to work, eventually lost his job and lost his apartment (I'm guessing his coworkers asked him to leave when he couldn't pay rent). Moved back in with his parents and still, just ... gaming. All the time. He'd just spend whole days sitting in front of WoW or some other video game. For three years that was all he did.
Eventually, his parents had to SHUT OFF THEIR INTERNET and have an intervention to reach him. Obviously I don't know the full story of what happened, but after that he did start to pull it together.
Got back into school at 29 and just recently graduated with a business degree. He's managed to "stay clean from games" (his exact words, BTW) for the last seven years. I can't imagine what an immense struggle that must be considering how ubiquitous they are now.
All told he lost more than 10 years of his life.
The whole time I'm looking on at this and thinking, if he was drinking, we would call this alcoholism. But what do we call it when it's video games?