id Software: Let's make a pioneering 2.5D shooter. (#Doom)
Raven Software: Oh, cool engine. But what if we added the ability to look up and down, and sometimes fly? Oh, and let's add inventory. And maybe some randomized ambient sounds. And interactive environments. (#Heretic)
Also Raven Software: You know what? Let's also add character classes. And make the gameplay more nonlinear, with going back and forth between maps. And let's add jumping. And let's add some hacks to enable doors and walls to move horizontally, and add scripting. And monsters spawning randomly. (#Hexen)
EDIT: Oh, and animated backgrounds, and thunderstorms, and falling leaves!


