This extremely popular, extremely competitive genre exists in a perpetual state of conflict--the best multiplayer action games are paradoxically the ones that seem to hurt the genre's attempts at proliferation. After all, the best multiplayer action games are the ones that people continue to play for years, during which time they have little need for other games. A number of excellent multiplayer action games were released this year, each in turn promising to last a very long time on servers around the world. Here are the nominees for Best Multiplayer Action Game of 2001:
Nominees:

Operation Flashpoint: Cold War Crisis

Publisher: Codemasters
Developer: Bohemia Interactive
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The large environments, variety of vehicles, and good team AI all contribute to the tense, realistic feel of the Operation Flashpoint multiplayer experience.
Return to Castle Wolfenstein

Publisher: Activision
Developer: Gray Matter
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Return to Castle Wolfenstein is well worth buying for the multiplayer game alone, so the fact that you get a solid single-player game in the box can only be considered a bonus.
Serious Sam

Publisher: GodGames
Developer: Croteam
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Serious Sam is fast and stable over the Internet, and while the deathmatch modes can be fun, going through the single-player levels cooperatively with other live players is especially enjoyable.
Tom Clancy's Ghost Recon

Publisher: Ubi Soft
Developer: Red Storm Entertainment
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Ghost Recon's multiplayer requires teamwork, strategy, and tactics and makes for a very intense competitive or co-op experience when it all comes together.
Tribes 2

Publisher: Sierra Studios
Developer: Dynamix
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It's with the large team games that Tribes 2 is really impressive. The scale of these games is unmatched, and the wide variety of team roles for players means there's always plenty to do.