Activision Blizzard (NASDAQ:ATVI) shares have lost more than 12% of their value since Sept. 3. Destiny, the video game publisher's much-anticipated first-person shooter, generated hundreds of millions of dollars in sales during the first few days following its release, but critical reviews have been less than stellar.

Currently, Destiny holds a 77 rating on Metacritic, a review aggregator. Although a 77 suggests a generally positive reception, it's quite disappointing for a game of Destiny's caliber. (Some context: In its legal agreement with developer Bungie, Activision had included a clause allowing it to terminate the Destiny publishing deal in the event that Bungie's then prior game, Halo: Reach, did not score at least an 80.) With plans for three sequels and several major digital expansion packs, the long-term financial consequences of a disappointing debut could be severe.

Still, there's reason to like Activision: Beyond its staple franchises like Call of Duty, the company appears to be sitting on two, largely unappreciated, potential blockbusters.

Hearthstone has quietly racked up 20 million players
Although its rivals have managed to capture the general population's attention with hit mobile games like Plants vs. Zombies and Candy Crush, Activision has been reluctant to embrace the mobile gaming trend. In the past, CEO Bobby Kotick has explicitly downplayed the long-term potential of mobile gaming, defending Activision's commitment to traditional console and PC games.

Until now, Kotick's logic has largely been sound -- the history of mobile gaming is one of relatively short-lived fads. Once seemingly mighty franchises like Angry Birds have been tossed aside by new games and new business models. Yet Activision appears to be sitting on what could become the most consistently profitable mobile game ever -- Hearthstone: Heroes of Warcraft is unlike any other mobile game that has come before it.

For the last few months, Hearthstone has existed in sort of an open beta period -- though it's officially been released, it hasn't seen widespread availability on mobile platforms. The game is clearly designed for touch controls, but has primarily been confined to traditional PCs. Admittedly, Hearthstone was released for some models of the iPad back in April, but has not made its way to the far more popular iPhone or Android platforms.

But that will change soon -- the game's lead designer told video game publication Joystiq that Hearthstone would make its way to all major mobile platforms by the end of the year. Despite being limited to the PC and iPad, Hearthstone has already attracted 20 million players, and its popularity could grow exponentially when it finally arrives on iPhone and Android.

Like other popular mobile games, Activision's Hearthstone is free-to-play -- instead of charging for the title upfront, Hearthstone is monetized with in-game transactions. But unlike many other popular mobile games, these transactions are largely optional, and do not affect one's ability to play the game. With Hearthstone, there's no sense of "pay-to-win," which may be why the game has attracted generally glowing reviews (currently, the PC version holds an 88 on Metacritic). At the same time, a competitive, semiprofessional scene has sprung up around the game -- something no other mobile game has experienced.

Despite the fact that payment is optional, Activision's management has said Hearthstone could generate as much $100 million in revenue per year. That number, however, could be woefully understated -- Activision moved away from the $100 million estimate on the company's last earnings call, noting only that the game had far exceeded their expectations. Rather than another flash in the pan, Hearthstone could emerge as a reliable cash cow for the company for many years to come.

Activision takes on the MOBA
Heroes of the Storm is Activision's second potential blockbuster, and like Hearthstone, it's also free-to-play. Rather than a mobile game, however, Heroes is clearly a traditional PC title -- one aimed at the tens of millions of MOBA fans.

The MOBA, or multiplayer online battle arena, is a relatively new genre of video game that has seen its popularity grow exponentially in recent years. The genre's two most popular titles -- Dota 2 and League of Legends -- have tens of millions of players and generate hundreds of millions of dollars in revenue. In fact, League of Legends was one of the top grossing free-to-play game last year, bringing in over $600 million.

Both games have large and rabid fan bases, with big professional scenes and tournaments with multimillion dollar prize pools. The recent, near $1 billion, sale of Twitch may not have happened if it weren't for these games -- they're consistently the most commonly streamed on the service (Hearthstone often comes in third).

Heroes of the Storm has no set release date -- it's currently in closed alpha testing. There's no guarantee that it will generate League of Legends-like results when it does launch, but the opportunity is certainly there for a billion dollar franchise. It will face tough competition, but Activision's Blizzard studio is well-known among the PC gaming community -- its past games, including World of Warcraft, Starcraft, and Diablo III, are among the top-selling PC games of all time.

There's more to Activision than Destiny
It can't be ignored -- Destiny's poor critical reception does not bode well for Activision's future. Still, there's much more to Activision than Destiny. With shares down so significantly since the game's release, Activision investors may be overreacting -- and overlooking a pipeline of games that could be poised to deliver stellar results.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.