Last Friday, Blizzard officially unveiled the Mists of Pandaria, the fourth expansion for its video game juggernaut World of Warcraft.

It's an Asian-inspired departure for the series, which has brought players to the traditional caves and castles of the medieval fantasy setting, along with otherworldly alien environments with influences that span mythology and science fiction. The centerpiece of the new expansion is the playable Pandaren, a humanoid panda species that is reminiscent of the Kung Fu Panda movie franchise.

But the Pandaren actually date back to Blizzard's 2002 title, Warcraft 3, which mentioned the Pandaren Empire in an April Fools joke, and later added the beer-chugging Pandaren Brewmaster hero, offering humor, durability and elemental attacks. Now, the Pandaren are set to become a major part of the world, complete with their own continent and character class, the Monk, which is partially inspired by the Brewmaster.

Mists is a radical evolution of the franchise, but Blizzard's willingness to experiment is a core part of what has made World of Warcraft, or WoW, a notoriously addictive game for nearly seven years. And the release of Mists - which could come as early as next year - comes during a crucial time for the franchise, which has lost almost 10 percent of its subscriber base in recent months. (Blizzard, as a rule, does not announce definite release dates until very shortly before the game is released.)

While WoW's dominance remains indisputable, In August, the total subscriber base fell to 11.1 million, a loss of some 800,000 subscribers this year. Blizzard CEO Mike Morhaime said at the time that the decline was a natural trend for the expansion's life cycle, and reflective of players getting through new content - typically new dungeons and bosses - and losing interest.

As our players have become more experienced playing World of Warcraft over many years, they have become much better and much faster at consuming content, he said. And so I think with Cataclysm they were able to consume the content faster than with previous expansions, but that's why we're working on developing more content.

WoW's genius - but potentially the game's Achilles heel - is a repetitive structure. Players don't simply run a dungeon or collect a crafting material once - the key to obtaining or creating powerful items is repeated efforts. Each week, the game's major endgame challenges reset, meaning defeated bosses are available to kill over and over.

This means that the most dedicated players will invest a significant chunk of attention each week to continue to amass various equipment, which helps the invidual player and group defeat even greater challenges. But with the game's current expansion, Cataclysm, only having a few dungeons released over the course of the year, frequent raiders, as the players are known, will steadily amass the best equipment until there is no strong incentive to continue to play. Burnout is also a common occurence, as supremely dedicated players must plan raids days in advance and prepare for hours of boss attempts.

Blizzard is doubly challenged to both retain longtime WoW players, while still inticing new players to try out the game by presenting an attractive entry point. For new players, that comes with the option of starting a new Pandaren character. For veterans, Mists will introduce sidegames such as a pet battling system, strongly reminiscent of Nintendo's Pokemon franchise, and challenge modes for the smaller dungeons that push players to complete levels quickly.

Player versus player combat will also be a major focus of the game, offering an additional way to amass loot. But there is already backlash against the Panda theme of the new expansion, with some fans who feel the focus - which again, started as a joke - is at-odds with the existing game. Some older players have already complained that the current WoW is too easy, as Blizzard has taken steps over the years to make the endgame more accessible to a broader base by lowering raid sizes and difficulties.

However, Blizzard's next game will not be Mists, but rather Diablo III, the third game in its best-selling action role-playing series, slated for a first quarter 2012 release. With the risk of competing against its WoW base, Diablo III will instead be given free to World of Warcraft subscribers - but only those who sign up for 12-month commitment, which can cost up to $180 total. Clearly, Blizzard is willing to give up a one-time profit of around $60 for a yearlong dedication.

It's a bold gambit on Blizzard's part, although the possibiity of Diablo cannibalizing WoW's player base is a real possibility. Both titles have fantasy elements, swords-and-sorcery-style gameplay and a hoard of item rewards,  although Warcraft has thousands of players per realm, or game world, while Diablo has a maximum of four players per individual game world, although players can switch to play with different players.

Another major difference is itemization: in WoW, the best items come from the half-dozen bosses that inhabit , and their statistics and effects are pre-determined, so players know what they can get if they invest hours of gameplay. Diablo III's best items are completely randomly generated, meaning they can drop from virtually any of the thousands of monsters that inhabit each world.

A controversial feature in Diablo III will be a real money auction house sanctioned by Blizzard, which will allow players to buy the best items for real American dollars and other currencies. But rather than selling the items themselves, Blizzard will simply facilitate the transactions with a database and auction tools, taking a flat fee for each item sold. Such an auction house would be seen as sacrilege in WoW - buying items is virtually impossible because the best items are untradeable - but Diablo's random nature means that trading is a central component.

Looking forward, WoW's lifespan seems inevitably limited. It's widely expected that character levels caps will be ultimately capped at 100, meaning that Blizzard has room for two more expansions after Mists, if they continue to increase the level cap by 5 each game. Blizzard is also at work on a next generation massively multiplayer game, codenamed Titan, but no details have emerged.

Will Mists of Pandaria revitalize World of Warcraft, or is the franchise on the way out? Share your thoughts in the comments.