Not the Gamer, but the Game
Computer or other video games, much like everything else in the universe, have both pros and cons that mix together to form a whole. A gamers health, intellectual, psychological and physical health are all affected by video games. I believe some, certain, computer games can be harmful to players, and some games can be beneficial. Violent and competitive video games may have a negative impact on a players psychological development. Other video games that encourage social interaction and diverse stimulation such as puzzle games or other brain games may have a positive impression upon a players intellectual and psychological growth. A persons physical growth and development also have both ups and downs from the effects of playing video games, depending on the game chosen to play. 
Firstly, violent video games have been shown to reduce the brains response to violence and cause and increase in aggressive behavior in youth. This has been all but forcefully proven through hundreds of scientific studies throughout the world. This not only blatantly says video games can be bad for players brain activity but increases their likelihood to be aggressive, which directly affects a persons health. 
Some studies show that violent video games alone do not inspire aggressive behavior, but the addition of high competition is also a large factor. Competitive video games can cause powerful negative emotions amongst friends. One gamer explains how he and his wife play video games together with another couple. After competing with the other couple, there was a creation of negative feelings leading to the two couples losing their ties. 
On the other hand, cooperative games promote healthy social interactions and foster altruistic demeanors among players. Most gaming time is spent face to face, with a friend or family member. When the gamers are working together to reach a common goal, instead of competing against each other, positive relations are created. Also, outside of face to face gaming, people post wikis, write blogs and even devote events towards gaming to share their experiences, progress, and problems. In this situation, they can help each other and work together, applying social skills otherwise left behind in completion. 
Also, gaming together, in a cooperative matter, can generate positive stress, or eustress. This happens when people voluntarily experience unnecessary obstacles, which is what gaming is. When a person is in control of how a situation is handled, to overcome obstacles and reach a goal, the challenge creates stress. This stress is actually good for the body and helps one feel energized, confident and relatively well-off. This harbors ambitions, positive thinking and goal-oriented living. There are also video games designed to help stroke patients recover and autistic children learn life skills amongst others. 
Physical development may be hindered, but also may be fostered depending on the games chosen today. There are several games designed to get people up and moving around instead of sitting or lying while gaming. While others are doomed to be a hands move only type of game. If chosen correctly, people can actually lose weight and increase physical strength and endurance while playing games. Hand-eye coordination has increased among youth in the last few decades. Some studies suggest that obesity and other related complications are a result of gaming for too long. 
On average, by the time an American kid reaches the age, 21, he would have played 10,000 hours of online gaming. This is the same amount of time spent in middle school and high school combined. If this time is spent sitting, eating junk food and competing on violent video games, then one could be an obese, aggressive, anti-social predator. On the other extreme, if one plays cooperative, non-violent games that require physical interaction, then he could be a fit, healthy and bright individual. The truth is, most gamers are in-between. There is always a grey area; situations are logically never black and white only. People might decrease their response to violence at the same time learning how to interact and play well with others. There will always be pros and cons to gaming, but how extreme the effects are completely dependent on the game chosen.