Each game in a Japanese Game Center is going to cost you at least 100 yen, with the most expensive costing 400-500 yen. Don't expect a manned counter to handle money exchange transactions for coins--machines will do that for you. Most game centers are laid out by types of games (see below), with the things for casual gamers more easily accessible, and the things for hardcore gamers in the back areas. Games of Chance are typically kept in less trafficked areas.
With that, here are the types of games you'll find...
Traditional-style Arcade Games
Trading Card-compatible Games
One of the new trends in Japanese game centers is to see arcade games that respond to customer-derived trading card input. Dragonball Z and Pokémon are two examples--in each of those, gamers can bring in their own cards and deploy them over the course of a computer-driven dual. It is a personalized experience, but it certainly can be daunting for the casual (non-card carrying) gamer.
Anybody who has been in an arcade or has seen Toy Story knows about claw games. Of course, Japan takes it to another level. The merchandise in UFO catchers can range from the relatively worthless to items that could fetch upwards of 5000-10,000 yen if purchased in a store. Further, UFO catchers have transcended merely the claw, as there are number other mechanisms (springs, pulleys, etc.) that some machines will let you manipulate to try to liberate some toys or other goods from the inside of the machine.
Anybody who has traveled to Japan or followed Japanese pop culture at all in the past ten years is likely to know about Purikura, or Print Club, machines. In the past, you were lucky to find one or two machines, but nowadays, a game center can't stay in business without at least three or four. Some places will even have changing stations. Be aware that some game centers have "women's only" purikura areas, so all you male readers out there, mind your surroundings!
Games of Chance
Although there is a push to make casinos legal in Japan, gambling with money is still illegal. However, that does not mean that games of chance of illegal, provided they have you use something other than real currency. In game centers, you'll exchange money for tokens. Those tokens then are used for games like Slots and simulated Horse Racing.
So there you have it--the basics for a Japanese game center. Hopefully you faithful readers out there (both the gamers and non-gamers) will now feel comfortable going into Japan's game centers and enjoying some of the fun and unique games!