For one thing, audiences have flocked in recent years to multiplayer online battle arena games, a very different style of game. These "MOBAs" are action-oriented strategy games in which opposing teams attack one another's bases.
The most-played MOBA is League of Legends, with 67 million monthly users, according to developer Riot Games. About 7.5 million gamers play during peak hours, more than the total number of World of Warcraft subscribers.
Another thing: These games are typically free to play, with developers making money when players buy premium virtual goods and upgrades. League of Legends (made by Riot Games) earned $946 million through October, according to SuperData Research, compared with World of Warcraft's $728 million haul. That's particularly important in emerging markets, where subscription costs can be a significant barrier to entry.
SuperData Research expects revenue from free-to-play games to grow nearly 50 percent to $11 billion in 2017. During the same period, it sees pay-to-play sales slipping about 40 percent to $1.7 billion.
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Blizzard is expected to launch its own MOBA called Heroes of the Storm, featuring characters from its World of Warcraft franchise next year, and it's widely expected to be free-to-play.
"It's a big play for them. It's also a tough play. How do you break into a market that's so saturated with League of Legends and Dota?" said van Dreunen, referring to the second most popular MOBA.
Pachter said that only a small minority of League of Legends players are Blizzard fans, but those who are will likely try Heroes of the Storm. Blizzard can attract others by leveraging its experience operating tournaments, he said, adding that top MOBA players could be enticed to switch games with the prospect of big cash prizes.
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Blizzard has already had success with free-to-play games. About 20 million people have registered to play its new digital card game, Hearthstone: Heroes of Warcraft. Launched in March, it has earned $114 million through October, according to SuperData Research.
It's possible that World of Warcraft will eventually transition to free-to-play, but analysts said Activision Blizzard won't make that decision soon.
"It's unlikely we see a dramatic change on the World of Warcraft business model any time soon," said Williams. "World of Warcraft is unique in terms of its ability to grab a large base of players who are willing to pay a relatively substantial monthly fee."