Fortnite is a force. The free video game is played by millions, and has reaped billions of dollars.

Survival is the simple goal of the multi-platform game that launched on consoles less than a year ago, and on Apple’s iOS operating in April. In each game, 100 players compete to be the last one standing.

According to SuperData Research, the game took in $318.3 million in revenue in May alone, and is on track to earn $3.5 billion this year for Epic Games, Fortnite’s North Carolina-based studio.

“Fortnite is incredibly beautiful visually. It’s got a Saturday morning cartoon-like feel and it’s very accessible, “ GameSpot vice president and general manager Ben Howard told CNBC’s “On the Money” in an interview.

“The game is completely free to download and play, with all the monetization coming on cosmetic items that don’t affect the gameplay,” Howard explained, such as ” a costume, a hat for your character, that kind of thing.”

Howard admitted he’s spent some of his own cash on Fortnite accessories, costumes and dance moves for his avatar.

“Sometimes you want that skin for your character. You want that superhero outfit, you want that cowboy outfit. You know, it’s hard to say why it’s compelling. But it is.”

Fortnite’s success comes as the World Health Organization is reporting that compulsive video game playing could be a mental health problem.

The U.N. health agency is classifying “gaming disorder” as when playing takes precedence over other daily activities and interests. The WHO states the condition is very rare, with about 3 percent of all gamers believed to be affected.

“I think that’s right, anything that’s as compelling or visual exciting as video gaming definitely has that potential to have people spend more time than maybe they should,” Howard told CNBC.

For parents of gamers, he suggests moderation and engagement, “in a way that you would engage in any other media consumption. So Netflix, YouTube, whatever it is, it’s important that parents understand you can definitely have too much of good thing.”

And Fortnite is certainly a “good thing,” with casual and hardcore gamers, as well as spectators.

“Another really vital part of why Fortnite has become so successful — it’s a game which is as compelling and exciting for people to watch as it is to play,” Howard said. On sites from Twitch to YouTube, “people are joining these streams by the hundreds of thousands. People are watching people compete.”

Howard described a recent celebrity Fortnite tournament in Los Angeles where “ high profile streamers teamed up with basketball and pop stars.“

“That has been a massive part [of why it’s] so successful. It’s really crossed over to pop culture, the zeitgeist.”

Epic Games says 125 million people have played Fortnite since it was launched less than a year ago.

Howard says when the game is released on Android systems, expect bigger numbers.

“Once they launch on the other main mobile phone platform, that will increase it again,” he added.

On the Money airs on CNBC Saturday at 5:30 am ET, or check listings for air times in local markets.