But the most interesting feature of Axiom Verge is also the strangest. About an hour into the game you'll acquire a new weapon called a glitch gun, and the name really says it all: you can use it to cause aspects of the game to glitch out and behave in unexpected ways. For instance, you can turn a floating bubble solid so you can jump on it and reach a high platform, or you could shoot an enemy and cause it to slow down, making it easier to kill. Different surfaces and creatures behave in different ways when glitched, and it’s a lot of fun to experiment. It's a novel feature, and one that was inspired by the hidden glitches in old NES games and tools like the Game Genie, which let you use cheat codes to change elements of a game. "It's all about trying to give players the exhilaration that you've done something you're not supposed to," says Happ. "I was trying to get that feeling in there, but on purpose."

The game constantly drops hints like this, showing parts of its world you won’t understand until much later. Much of the joy comes from those "a-ha!" moments when you get a new skill and realize exactly where you can use it. It's a hallmark of the genre, known as "Metroidvania" — named after Metroid and later Castlevania games, which use a similar structure. But Axiom Verge differentiates itself in a few ways. For one thing, there's a relatively large focus on combat; you're still constantly exploring new areas, but each new section is filled with a host of aggressive alien creatures, from flying squid to scorpions that shoot missiles from their tails. The gunplay is reminiscent of classic run-n-gun shooters like Contra, and the variety of weapons and bad guys keeps things fresh — the giant boss creatures, in particular, will force you to use your entire arsenal in order to defeat them.

Axiom Verge starts with your death. You play as a young scientist who dies in an accident, only to wake up in an alien world unsure of how he got there. The set-up captures that same feeling as the early Metroid games: you're all alone on a strange planet, where everything wants to kill you. The only way to survive is to explore. The world of Axiom Verge is made up of many smaller areas all connected together on a large, complicated map. As you play you'll uncover dead ends and strange objects you can't interact with — at least not yet. The game slowly gives you new weapons and abilities that can be used to access new areas. For instance, very early on you'll come across a completely empty room, and soon after you'll get a drilling ability that lets you break through its blocks, opening up a new route in that former dead-end.

Axiom Verge has been in development since 2010, though it initially started out just as a hobby. Happ previously worked at a number of game studios, most recently Petroglyph Games, and he liked to work on new game ideas in his spare time. Whereas most people unwind with some TV at the end of a long day at the office, he would tinker with prototypes. But prior to Axiom Verge, he never stuck with any one idea for very long. This new game idea was different. "My interest never seemed to die off," he says of Axiom Verge.

"It was very disorienting."

After two years of working on the game, he was still viewing it as a sort of hobby. It wasn't until he showed it to the world that he realized it was an idea worth pursuing seriously. On April 10th, 2012, he uploaded his first video to his previously dormant YouTube account and tweeted a link out to his seven or so Twitter followers. It was the very first trailer for Axiom Verge — and before the day was out, it was picked up by a number of gaming sites, eventually getting featured on bigger outlets like Gamespot. The attention only grew from there. "It was very stressful," Happ explains. "I had trouble sleeping. My phone was constantly buzzing from notifications, that people were emailing or talking to me on Twitter. It was very disorienting."

Clearly a lot of people were waiting for this kind of game, but he wasn't sure what to do next. There was still a lot of work to be done on the game, and Happ was still working at his day job to pay the bills. Many people tried to convince him that Kickstarter was the way to go, but Happ was wary of the added pressures that comes from a crowdfunded game. "I was especially intimidated by the Kickstarter trailer, where I film myself in an office trying to pitch it," he says.

So he decided to hold out for a deal that made sense for him, and spent the next two years continuing to work on the game. Eventually he signed with Sony's Pub Fund initiative, which let him work on the game full-time. That was in 2014, and by then Happ says he had only created about 25 percent of the game — working alone had put him in a bit of a rut. But when Sony started showing the game at festivals and events, Happ was finally getting the outside feedback he wanted to get the game where it needed to be. "It really helped a lot," he says.

Development took nearly a half a decade in total, but the resulting game is fantastic. Happ may not have set out to make a new Metroid-style game, but he managed to capture much of what makes the series so beloved, from the satisfying exploration to the moody sense of isolation. And with new elements like the glitch mechanic, Axiom Verge feels both retro and new at the same time. It’s impossible to escape the game’s influences, but that’s not necessarily a bad thing — playing Axiom Verge reminds me of the first time I explored the planet Zebes, all those years ago.