You get all the latest and greatest games. And this is usually for new games aswell. Girls go there, and they actually play the games instead of watching. They are actually really into the video game scene, just like guys. The game centers there are more popular than in other countries.
People use game centers to chill out from a hard days work, or to meet girls.
Often, big game centers are the main meet up points for groups going out for the night, like e.g instead of the McDonalds in the town. Some places get really packed out. They actually have link-ups in Japan. For example, if you played StreetFighter, there would be an identical machine behind the one you where sitting on, so people could sit down and challenge you, and you would never know who whupped your arse with Dhalsim. So this makes it less hassle to challenge people to Tekken Tournament, as you don't won't to sit next to some freak who skitzes on you when you kick his arse.