Doom by ID software was the game which put 1st person shooters on the map,
though Wolfenstein was the first. Doom introduced many important new features:
Non-orthogonal walls, lighting, better AI, multiplay, full texture mapping, and
a chainsaw. The pseudo-3d engine made the graphics the best yet seen on the PC.
One of the great things about Doom was the ease with which it can be modified.
There are many editors and utilities about to enable you to change just about
everything from the levels to the graphics and sound. This was particularly
useful for making death match arenas. Pictured here is Deu - a Doom map
editor. Many 'wads' are available with multiplayer levels not dissimilar in design
to quake3's arenas.
Chilloutgames