It's 25 years to the day that iD software released Quake, the classic first-person shooter featuring a fully 3D world (including characters!), mouselook (not enabled by default!), and an outstanding soundtrack by Trent Reznor.
Until Quake, state-of-the-art first-person shooter games on PC generally used 2.5D graphics techniques to simulate height and depth while usually restricting player movement to a two-dimensional plane. Quake broke the mold by introducing a fully 3D polygonal universe populated with 3D objects and monsters, giving players six degrees of freedom in an immersive virtual world. Unlike 1993's Doom, you could look around freely (and even jump) in Quake.
"It was an obvious progression from Wolfenstein's three degrees of freedom to Doom's four degrees of freedom, to Quake's six degrees of freedom," Quake programmer John Carmack told How-To Geek. "Some Doom clones experimented with a shearing look up/down for five degrees of freedom, but if you are going to support arbitrarily oriented polygons, you might as well get all six."
A remastered edition is in the works, reports Notebook Check.
I remember the Quake billboards all over London in '96, convincing me that yes, it was time to buy a Windows PC. I can't find a single photo of those looming nightmare announcements online, which is strangely unsettling, but I did find this amusing magazine ad from Germany at about the same time.