"It starts with one..." -Chester Bennington

Alright it actually started with Wolfenstein 3D, but this is where first-person shooters got expansive. Any video game from 1998 is gonna be dated in some ways (in graphics and design), but Half-Life avoids many of those pitfalls and has managed to still be an overwhelming achievement. This shaped the future of video games with its narrative techniques, and Valve set another important bar for pushing the medium forward into the 21st century. This is coming out around the time of Goldeneye 007, Duke Nukem 3D, and Quake II, and its actual gameplay is so much more comprehensive and forward-thinking than all of them. Halo was just made in Half-Life's image, like The Christ in God's. That rail level still sucks though.