If you look at Wolfenstein 3D, Rise of the Triad, etc, they all have level geometry that could be drawn easily using graph paper. Rectangular walls means that e

If you look at Wolfenstein 3D, Rise of the Triad, etc, they all have level geometry that could be drawn easily using graph paper. Rectangular walls means that everything has a 90° angle. Doom on the other hand can have all sorts of interesting level geometry, as long as each individual node in the binary tree doesn't have any convex elements.