Romero and John Carmack develop techniques for smooth scrolling on PC games, a significant technical achievement at the time. This innovation is a hallmark of the Commander Keen series.

Romero played a crucial role in designing and implementing fast-paced gameplay mechanics in Wolfenstein 3D, setting a new standard for action games.

Romero's level design in DOOM showcased innovative use of textures, lighting, and architectural elements, contributing significantly to the game's immersive atmosphere and engaging gameplay.

Romero and id Software utilized the shareware distribution model to promote and distribute DOOM, revolutionizing how games were marketed and sold. He has been an evangelist of the shareware distribution model through all his career.