"I'm freaking out. It's wild," Randy Pitchford, head of developer Gearbox, tells BBC Newsbeat.

Borderlands is, quietly, one of the most successful game series launched in the past 20 years.

A mixture of first-person shooter and role-playing game, part one stood out in 2009 thanks to its cartoonish art style, edgy humour and co-operative multiplayer modes.

Players take on the role of vault hunters, tasked with gathering loot on an alien world where they meet a cast of wacky characters and over-the-top enemies.

The series has never swept an awards ceremony, but it's debatable whether it ever tried to.

Journalist Ash Parrish, of tech website The Verge, tells Newsbeat the game "turns off your brain and turns on the fun".

"The core ethos in Borderlands is that there's going to be a lot of shooting and a lot of dumb humour," she says.

"That's sometimes all you want out of a video game."

It's been a winning formula for the series, which has sold 94 million copies since the first game, putting it in a similar league to titles such as Tomb Raider and games based on the Harry Potter films.

"It shouldn't be as successful as it is," says studio boss Randy.