Doom was a tense collaboration between Carmack and Romero. Carmack was geniusing out the engine, while Romero was pulling hard on the game atmosphere, music, level design and details like the timer that spawned Doom's speedrunning culture.

Quake, which was Romero-less, was a technical masterpiece, but not a very memorable game. There was the brown level, the other brown level, and the brown level again but different. Its modding potential plus competent network code really made it a big hit.