Cons:
May lead to addiction or social isolation.
May have negative effects on mental health, including increasing anxiety and depression symptoms.

This all really depends on where one falls on a certain "made up" spectrum. There have been a lot more studies done that show the benefits of gaming on ones mental health, then there have been that shows the negative on it.

Video Game addiction is also a very debatable thing, as it's hard to determine whether one is addicted to a video game, and what addiction to a video game actually is. In fact VGA cases are lower than one would assume.

The social isolation part kind of goes hand in hand with VGA. If you suffer from any sort of addiction than you're going to socially isolate yourself.

When all is said and done the only definitive con of gaming is that it will leave your wallet more empty.