“Basically the reason I downloaded it is because a lot of my friends in the States have been going mad for it,” says Jon Norris. “They’re quite sensible adults but they were absolutely freaking out about it.”

Norris, head of content at Brighton-based digital agency Rocketmill, is talking about Pokemon Go. It’s a new augmented reality mobile game – and it’s taking the world by storm. The title, which has been available in the US for less than a week, has racked up millions of downloads already. The app lets players track down and “catch” virtual Pokemon that appear somewhere in the world around them.

Although not yet officially available in the UK, eager players like Norris have been able to install the app via some technical workarounds. The app has not risen to fame without controversy, though. For one thing, some have raised concerns over the fact that it can have very broad access to user data - from emails to search history and Google Drive - when users give it access to their Google accounts on iOS devices.

So what is the big attraction? And could its success have been predicted?

Admissions tests

Psychologist Andrew Przybylski at the Oxford Internet Institute has studied what attributes are essential for games to have the chance of being successful. These range from whether they are pitched at the right difficulty for players to how much they build in, or foster, social interaction with others, and he thinks one important factor is the ‘barrier of admission’ to having a good time.

A crucial feature of Pokemon Go, for example, is that it relies on technologies many people have and are already familiar with – their smartphone and GPS. Contrast this with geocaching, for example, which requires a more advanced knowledge of GPS (and even an array of physical equipment).

Many of the games that have enjoyed surprisingly broad appeal in the past – from Snake to Angry Birds and many of the original Wii titles – also married highly accessible gameplay with technology that was relatively new but easy to use, adds Przybylski.

“People have already learned how to use their phones – just like they know how to use their bodies for Wii Tennis,” he explains. “The work has already been done.”

“You can dive into it very easily,” agrees Norris.