Gaming has become more and more prevalent in our society, and adolescents probably are some of the biggest consumers of it. The positive and negative effects of gaming are an active area of research, and, like many new technologies, we're still not totally sure what to make of its effect on us. (Check out the links at the end of this post.)
My concern when it comes to gaming is its opportunity cost. Time spent gaming is time that could have been spent on other endeavors. So, for example, if a teen were having a tough time academically in school but playing video games for hours on end each day, some of that time could have been spent studying and completing homework.
But you could see the same downfall with any activity we do. Anything we spend vast amounts of time on means a sacrifice in other areas of our lives. Exercise, reading, socializing are usually thought of as beneficial activities, but, not done in moderation, they all can negatively affect other aspects of our lives. Too much exercise can wear our bodies down, too much reading can be isolating, and too much socializing can mean too little time for self-improvement.
One of the downsides with this comparison is that video gaming probably does not have the same level of benefits as exercise, reading, or socializing. Though some studies suggest video gaming has positive effects such as better concentration and working memory, these benefits do not seem as clear cut as the three activities mentioned above. Even without considering possible positive effects, video gaming still would be in the same category as any other harmless but not relatively unproductive activities such as watching a sitcom, riding a hoverboard, or reading gossip magazines.
Here are a couple different articles with various perspectives on gaming and its effect on our brains. (Of the three, the Dana Foundation article seems the most nuanced to me.)