Fallout Shelter, the widely popular – and still insanely addictive – mobile game released after Bethesda’s E3 conference last year, was the developer’s first mobile game – and, according to director Todd Howard, it won’t be their last.

In an interview with GameSpot during this week’s DICE Summit, Howard said the company is planning to invest more in the mobile gaming market. The team “never anticipated Fallout Shelter would enjoy the success that it has,” and didn’t expect they would “be number one and out-gross Candy Crush for a while,” saying such expectations led to “failure and disappointment.”

While Bethesda never announced how much Fallout Shelter made in microtransactions, research firm SuperData published that the game earned $5.1 million within “the first two weeks of availability” – pretty impressive, considering the game wasn’t designed as a “cash cow” for the developer. Rather, the developer was concerned with the experience the game could offer.

Mostly we were concerned with it being appropriate for who we are [as Bethesda Game Studios]–meaning it’s got a bit more meat on the bone than other things like it. But its overall popularity? We were not ready for that, which is a good problem.

Howard said that Bethesda’s “drive” to produce mobile games arises from the fact that the developers themselves play mobile games, which “naturally” inspires them to develop their own in turn. He didn’t specify what kind of mobile games they would produce – which could be anything from spinoff games of existing franchises to entirely new creative titles.

Fallout Shelter was announced during Bethesda’s E3 conference and released later that same day for iOS, with an Android version debuting a few months later.