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The following is taken from Wikipedia.org
Halo 2 is a first-person shooter video game developed by Bungie Studios. Released for the Xbox video game console on November 9, 2004, the game is the second video game title in the Halo franchise and the sequel to 2001's critically-acclaimed Halo: Combat Evolved. A Windows Vista version of the game was released on May 17, 2007, developed by an internal team at Microsoft Game Studios referred to as "Hired Gun". The game features a new game engine, as well as using the Havok physics engine; added weapons and vehicles, and new multiplayer maps. The game's plot, taking place in the 26th century, concerns future humanity fighting an interstellar war against a collective of xenocidal alien races, the Covenant. The player assumes the roles of Master Chief and the Arbiter, and fights enemies on foot or with a collection of alien and human vehicles.
After its initial release, Halo 2 was the most popular video game on Xbox Live, holding that rank until the release of Gears of War for the Xbox 360 nearly two years later. By June 20, 2006, more than 500 million games of Halo 2 had been played and more than 710 million hours have been spent playing it on Xbox Live; by May 9, 2007, this number had risen to more than five million unique players on Xbox Live As of November 2008, Halo 2 is the best-selling first-generation Xbox game with 8.46 million copies sold worldwide, with at least 6.3 million copies sold in the US alone. Critical reception of the game was generally positive, with most publications lauding the strong multiplayer component; at the same time, the campaign was the focus of criticism for its cliffhanger ending.
Unlike its predecessor, Halo 2 allows players to compete with each other via Xbox Live, in addition to support for split-screen and system link multiplayer. Halo 2's multiplayer mode offers changes from earlier online first-person shooters. Traditionally, one player sets his or her computer or console up as a game server or host, specifying the game type, map, and configuring other settings.The game software then uses a service such as GameSpy to advertise the game to the world at large; other players choose which game to join based upon criteria such as the map and game options each host is offering, as well as the ping times they are able to receive. In Halo 2, however, Xbox Live players do not choose to host public games, and they do not specify individual maps and options to search for. Instead, players select playlists that are geared to different styles of play. For fairness and balance reasons, certain gameplay aspects from the campaign mode are disabled or missing in multiplayer; for example, the Fuel Rod weapon is missing from vehicles and maps.
Technical lead designer, Chris Butcher, commented on the development of Halo 2's multiplayer in Edge, a British gaming magazine, in January 2007. Responding to a rash of subsequent news articles, Butcher clarified his position on Halo 2 multiplayer. He noted his original intent with the game, but he also reiterated disappointment. "For Halo 2 we had our sights set very high on networking," Butcher said. "We thought about the great LAN parties you can have with Halo 1 and decided to try [to] recreate that awesome experience of having all your buddies over to play, but using Xbox Live instead of having to lug consoles and televisions around. Going from having no Internet multiplayer to developing a completely new online model was a big challenge to tackle all at once, and as a result we had to leave a lot of things undone in order to meet the ship date commitment that we made to our fans."