Multiplayer games have been around for longer than you might think. The first examples can be traced back to the early 1980s, with massive adoption starting with the arrival of the Internet and the World Wide Web by the mid 1990s. Multiplayer games can offer the same multimedia values of single-player games while introducing other human players into the mix. That makes them a greater challenge and, in many peoples' opinion, more rewarding to play. Several formulas have evolved through the years, from the squad-based gameplay that was already present in the Essex Multi-User Dungeon (MUD) one of the first documented massively multiplayer games to human opponents that can be traced back to games like EA's Multiple User Labor Element (M.U.L.E.) from 1983.
The reason why multiplayer games have been so successful is that playing with or against an artificial intelligence cannot be compared to a human opponent. Additionally, the social component of a single-player game is virtually nonexistent.
One of the first viable examples of a multiplayer game was the Essex MUD, which was developed by Richard Bartle and Roy Trubshaw of Essex University in 1979. The original game consisted of about 20 rooms described in prose. Up to 250 players could coexist in this game world, so they could "see" each other in the room. Descriptive texts would state facts like "Peter is here," for example. Players connected to the MUD server using the EPSS network, which connected six British universities; and from 1980, players connected to the MUD server using the ARPA network from the United States. Compared with a modern game, Planetside (by Sony) supports more than 3,500 players per server.
The Essex MUD was a great inspiration for many developers. In fact, a very active MUD scene existed during the 1980s and part of the 1990s. MUDs faded away as graphical multiplayer games such as Everquest appeared. But for more than 10 years, they ruled the multiplayer arena.
However, MUDs were not the only way to go. Simple competitive games with human opponents created bigger challenges for the player, thus becoming a viable playing experience. A good and early example is M.U.L.E. In M.U.L.E., up to four players competed to conquer a new planet in a way not very distant from today's real-time strategy games. But the success of the game was limited, mainly because network infrastructure circa 1983 was not very well suited for real-time play.
The turning point came around 1993, when the Internet and more specifically the World Wide Web phenomenon exploded. In less than six months, the World Wide Web evolved from zero to infinity, taking the whole planet by storm. As a side effect, connection speeds were greatly improved, from the very early 9600bps modems to somewhere around 56kbps, and from there to ISDN, DSL, and cable. This speed increase was extremely relevant because it allowed developers to transfer all state information from one computer to another while keeping the gameplay fluid. Age of Empires, for example, could be played on a 56kbps modem, and that included dozens of units fighting against each other.
Today, multiplayer games have stabilized around two "orbits," which are direct descendants of MUDs and games like M.U.L.E. On one hand, MUDs gave way to graphical RPGs like Ultima Online and from there to Everquest, Asheron's Call, and many others. These games are all about immersion and socially interacting with a rich game world. Thousands of people actually live their lives inside each one of these games in a 24-hour alternate reality. In fact, these games are probably the most addictive of them all, with extreme cases counting for more than 1,600 hours of gameplay per year (that's more than four hours a day, even on Sundays). As a very intriguing side effect of the Ultima/Everquest phenomenon, real virtual economies have been created. Some fans have sold their properties or characters on auction web sites, often for respectable sums of money. This type of behavior should definitely make us think about the influence of the gaming scene on people's lives.
On the other end of the spectrum, reduced-scale multiplayer games have been successful as well. Here, a distinction has to be made between competitive and cooperative multiplayer titles. The difference is in the role of other players: Will they be enemies you must defeat, or will they be your teammates on a global mission? A title that clearly shows these two categories is the incredibly popular Counterstrike, which is actually a modification to the original Half-Life game. In Counterstrike, two teams fight each other, so there's competitive gameplay on opposite sides, and cooperative gameplay between members of the same side.
The future looks bright for multiplayer games. Network infrastructure keeps growing, and today most users already have broadband support that allows better interaction. Several middleware companies have emerged in recent years, enabling bigger and better games. Additionally, gameplay innovations are constantly introduced. Some people predict that multiplayer games will eventually engulf all other gaming experiences, so single-player games will just disappear. Although that's probably an overstatement, it clearly shows the level of expectations the industry has put in multiplayer gaming. But remember solo and team sports peacefully coexist in the real world, so there's really no need for single-player games to disappear in favor of multiplayer experiences.