Over the last year, the roguelike has become the it-genre, particularly for independent developers. While debate remains over what constitutes a roguelike or whether the term should even be used, there's no argument around the fact that both developers and players have come to love these games for their endless, procedural challenges.

This year's best student game in the Independent Games Festival was Risk of Rain; Klei Entertainment sold over a million copies of Don't Starve last year. These are just two obvious success stories that owe a lot to the appeal of roguelike mechanics.

Tanya X. Short of Kitfox Games (Shattered Planet) succinctly captures this appeal: "As a designer, and as a player, I love procedurally generated, system-driven games because I'm curious."

That hook has lead more and more to explore the boundaries of roguelike game design. "I think success breeds success," says Don't Starve lead Kevin Forbes. "There have been a couple of really good games in the past few years that serve both as an introduction for players, and as inspiration for developers."

"There's a book that could be written on this topic."

Daniel Cook, developer at Spry Fox (Road Not Taken) explains another key element of the genre -- its longevity. "I've been playing NetHack for well over 20 years. It is very much a hobby for me. The long-term variability, depth of mastery, and richness of evergreen surprising moments are an anomaly in this era of disposable movie games," he says. In fact, the roguelike -- from its history to its design space -- is so fruitful that "there's a book that could be written on this topic," he says.

"When some journalist / grad student / pundit asks 'What is the culturally relevant future of the game industry?' one loud and clear answer should be 'roguelikes,'" says Cook.

Why do players and developers love them?

The roguelike has caught on not just with developers, but also with players. Why is that? 100 Rogues developer Keith Burgun puts it down to a renaissance of players looking for games that offer rich play experiences -- which we can also see in the surge of popularity of everything from Minecraft to European board games, he suggests.

"I think people are just slowly, but surely, getting a tiny bit more ground about 'what games are.' They are realizing that games are fundamentally way more than just a Universal Studios theme park ride."

He continues, "I think they're starting to realize how important gameplay -- quality interactions -- are, and that's causing more and more of them to look in places that they wouldn't have before."

Short notes that players are attracted not to the idea of the "roguelike" per se, but the experiences these games afford to them: "People don't play first person shooters because they like the word FPS; people play FPSes because they enjoy shooting guns as an immersive experience."

"What I love as a player is that I'm constantly running into new situations that I want to share with my friends," Cook says. Short agrees: "Their value tends to be in providing the maximum possible array of outcomes... i.e. satisfying novelty as long as possible, with the minimum number of elements."

Burgun notes that this novelty can speak to gamers in a very basic way, with roguelikes offering "so much stuff in one package that surely something in there, you're going to enjoy."

"As a player, I feel like any given mechanic or system can reliably be pushed to its limits, as a challenge and as a strategic tool."

"You can be surprised by something new every time you play. You can challenge yourself to learn about and master complex systems," Forbes says. "I think that a lot of players really appreciate being able to direct their own experience, and emergent gameplay lets things happen that keep the experience fresh. There's a level of replayability inherent to the genre that's sorely missing these days."

The roguelike allows for "unique, surreal and wonderful collisions between player agency and complex systems," says Cook, a mode of expression that is "unique to games."

Forbes continues this thought: "I've always found it odd we game designers have such an exciting, unique medium to work with, but so often waste its potential trying to emulate film."

It's the potential for surprise that can excite both the player and the developer, Short says. "As a player, I feel like any given mechanic or system can reliably be pushed to its limits, as a challenge and as a strategic tool. And as a designer, it's incredibly satisfying to watch players use your systems to come up with new strategies you didn't think of."

Developer appeal goes further than that

But its appeal for developers extends well beyond that: Roguelikes provide an exciting creative space, certainly, but the genre also allows today's smaller teams to stretch their resources.

"I think every designer now has to ask themselves, at the start of any game project these days, 'Is there any way I can procedurally generate any of my content without the quality suffering enormously?' Any answers to the affirmative must be taken seriously. The value-to-cost ratio is just too high," Short says.

Cook puts it more succinctly: "One- or two-person teams can't afford to make 100 hours of sexy 3D-storytime. But they can make 100 hours of roguelike bliss."

"One- or two-person teams can't afford to make 100 hours of sexy 3D-storytime. But they can make 100 hours of roguelike bliss."

The savings is not simply based on the fact that content is generated procedurally and thus, in some sense, free -- the thinking required to create games like these also insures design changes won't result in costly rework, says Cook. "With static levels, a change to your core mechanics could result in months of rework," Cook says. "Regenerating levels after a change to your game mechanics is a trivial exercise. Content becomes amenable to cheap refactoring."

That flexibility also results in a fundamentally different kind of gameplay, says Defender's Quest developer Lars Doucet. "In most other games, you can always reset, or reload, and use your knowledge of the future (or of unchanging levels) to march your way forward. Most video games are like karate katas that you practice over and over again. With roguelikes and procedural death labyrinths, it's an actual fight on the streets -- you don't know what's coming at you, and you have to improvise and think on your feet."

This procedural flexibility, in concert with mechanics like permadeth that the genre has popularized, "opens up the possibility for single-player video games to actually be contests -- to be competitive -- to be a thing you can win and lose," notes Burgun.