If you have a FAST computer, you need to take a look at Unreal. It has great graphics and realistic effects. One thing about a lot of computer games is the eventual predictability of the computer as an opponent. With multi-player games like Quake, though, this is hardly the case. Since you are playing against real people, unpredictability is built in.
Many people play on their modems and link to shared servers.
Despite the constant evolution of game technology, many people stay with games like Quake, even preferring Quake I to Quake II for what they consider its playability. This means that it is easy to get more layouts and add more players to a versatile basic, and you don't need super hardware to enjoy fundamental things like logic, reason and killing the other guy. Although many games can be visually dazzling, they are not challenging over any time period. Do prepare to be slaughtered, however, as they generally show no mercy. Play on your own, or with some friends on a modem or on an internal network.