1 ADDICTION
Games these days are made to be extremely addictive, the scenarios, colors, noises in certain games all have an extremely psychologically addictive influence on the human brain. The games are now being designed to reward addiction not your play ability, you are rewarded with online experience points, rewards for the total time online and not your level of skill, some studies suggest games like Call of Duty, World of Warcraft etc are as addictive as cigarettes or cocaine
2 BODY HEALTH
Sitting in one spot is very bad for people's bones, muscle, posture and circulation. People who sit in front of a screen generally are not eating properlyWe all spend too much time at the office or studying for the next exam so why spend free time sitting in front of the computer
3 GEEKY NERDY PERSONALITY DISORDER
Life stinks and the world sucks but so what? You still need to file your taxes, do your work, feed your neighbors pets when they went on vacation and get on with the general drudgery of everyday life. Gamers are sometimes just way too disconnected with reality, just as the ex-girlfriend of an obsessive gamer with all the BS they had to go through in their realtionship
4 WASTE OF FINANCE , getting too far into the gaming world can lead to loss of ambition at work, serious debt cos some games are based on gambling like poker, other games take your credit card for the time you spend on their online networks and collecting games and consoles is an expensive hobby
5 MENTAL HEALTH, a large percentage of people with very bad social mental problems are now coming from gamer backgrounds, you have crazy formals draw up by doctors (tech addiction from youth, with Tetris Effect + violent media content +/- psychotropic medication + deprivation of touch with nature = formula for disaster
That said I'm a gamer myself
I think games are fascinating, its an artform, entertaining and games have brilliant worlds where people play in a new progressive media
but all nearly games come with a warning
It says to play them only for 1-2 hours at maximum exposure, it warns you about this when you install the game or its in the playstation and xbox handbooks
Like all things, the gaming entertainment industry should be taken in moderation