"Imagine if [id Software] had made Doom and Quake, and then nobody made another first-person shooter for 15 years."

Chair Entertainment founder and creative director Donald Mustard used this inconceivable scenario as an explanation for how Shadow Complex came to be. The 2009 Xbox Live Arcade spy game plunged players into a freely explorable 2D world, stepping away from the vivid 3D experiences that were so popular at the time.

It was the first real example of old-school game design sensibilities being enhanced with the power of modern hardware. It was Super Metroid, reborn.

"I think that 2D game design hit its pinnacle in Super Metroid, which came out in 1994," Mustard told Mashable. "This was right near the end of the Super Nintendo. Right before the PlayStation came out, before the Nintendo 64 came out, before games became all about 3D.

"[Super Metroid's] non-linear, almost open world 2D game design was so amazing. And then we just forgot about it for like, 15 years."

There were other Metroid-style games in the years between 1994 and 2009, even a number of popular ones like Castlevania: Symphony of the Night. But Shadow Complex re-oriented the genre with its modern look, and it was an instant Xbox 360 hit. Now, six years later, it's back and it's looking better than ever.

"It's always been our goal to bring Shadow Complex to a wider audience," Mustard said. "It's very near and dear to our hearts. We've been looking for the right opportunity to present itself, and that moment finally came a few months ago.

"We've been working hard to get the game up and ready and working on all these new, cool platforms. That will hopefully pave the way for future games as well."

Shadow Complex Remastered is available for the month of December as a free download from ShadowComplex.com. Then, starting in early 2016, it'll be sold on PlayStation 4, Xbox One and — for those that don't take advantage of this month's free offer — as-yet-unnamed PC storefronts.

The newly remastered game is what Xbox 360 fans remember, for the most part. It looks and runs better than it did before, but Chair felt it was important to preserve the original experience as it comes to a new, wider audience.

"When we originally authored the game, we made a lot of the art and a lot of the textures at a much higher resolution [than the Xbox 360 could support], just because that's what we were seeing when we were working on the PCs making the game," Mustard said.

"This allowed us to go and turn all that source art back... on, to make it a higher resolution, to show the original art that we sourced it at. So that's all back in the game."

Along with the restored original art, Shadow Complex Remastered also moves the game into the latest version of the Unreal Engine software tools that were originally used to build it. That means improvements to lighting and other visual effects, and support for higher resolution — up to 4K, according to Mustard.

The story remains the same, but Remastered does make a few changes on the gameplay side, including an improvement to the game's close-quarters melee takedowns. In the original Shadow Complex, you could get close to an enemy and, with the press of a button, be treated to a cinematic face punch. Remastered injects some more variety.

"Now it's all contextual," Mustard said. "If you run up to someone and you're leaping through the air, and you hit the takedown button, you'll do a flying jump kick. Or if you're hanging on a ledge above someone and you hit it, you'll reach your legs down and snap their neck."

The remastered game also folds in a fresh lineup of Achievements and Trophies for players to unlock. And maybe some surprises? "A few other, little secrets here and there," Mustard said, without elaborating.

The game also supports keyboard and mouse controls for PC players, and Mustard promises that "a substantial amount of work" went into making them feel right.

Fundamentally, though, Shadow Complex Remastered is the same game it was in 2009. That's the whole point. The game's popularity has endured in the six years since it was released, even as Chair went on to achieve superstardom with its trilogy of Infinity Blade games.

"I'm really proud of what we did," Mustard said of the original Shadow Complex, adding, "and I'm so excited that the game can now be played by so many more people on their platform of choice."