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Dario Casali, a level designer at Valve, told Engadget that "[Half-Life: Alyx] started out as an exploration of VR rather than saying we're going to just work with Half-Life IP. After we shipped The Lab [a series of small VR experiences] and we were working on the Vive, we decided we were going to push into the VR space a little harder. And with the hardware we were developing, we wanted a big software app that would push the hardware along."

Surprisingly, Casali said the company didn't immediately jump to Half-Life as the ideal series to bring to VR. Portal also seemed like a good fit, especially since The Lab takes place within its universe. But the teleportation mechanics would have been difficult to bring into VR without making players queasy. Valve also excluded multiplayer games right off the bat, since there weren't nearly enough VR owners to make that worthwhile. Then the company built a 20-minute VR demo using assets from Half-Life 2, and everything clicked.

"With that demo, we realized that the Half-Life mechanics translated pretty well to VR, and in many cases they became even more compelling than we remembered," Casali said. "So based on the strength of that demo, and the interest that that revived in the company -- because everybody's very fond of Half-Life at Valve -- it wasn't a difficult sell."

As a series that's practically synonymous with gaming innovation, it also made plenty of sense for Valve to use Half-Life as its lens for exploring VR. The first title was a landmark achievement in unstructured narrative while Half-Life 2 and its episodes focused on physics and lighting in bold new ways. But after exploring ways to follow up on the cliffhanger ending of Half-Life 2: Episode 2, Valve simply chose to do... nothing. As co-founder Gabe Newell told IGN, the company didn't want to spit out another sequel to increase quarterly sales figures. But VR? Now, that's an interesting challenge.

Half-Life: Alyx builds atop the VR gameplay innovation we've seen from Valve and other developers over the past four years. But for it to truly stand out, it had to bring something new to the table. Enter the gravity gloves, which let you reach out and grab small objects in the environment. You just point your finger, flick your wrist and catch the item as it's flying toward you. It's a bit complex at first, but several hours into the game it practically becomes second nature.