Back in the day it was probably easy to move goalposts as techniques advanced. Do remember that Duke 3D's Build engine did not draw a true 3D environment by today's standards, and Novalogic's Voxel Space did not use voxels but a heightmap with painter's algorithm.
My personal opinion is that to qualify as 2.5D the game engine must internally use a 3D coordinate system even if the render process is 2D, and 3D requires a true 3D to 3D conversion.
Comments
Back in the day it was probably easy to move goalposts as techniques advanced. Do remember that Duke 3D's Build engine did not draw a true 3D environment by today's standards, and Novalogic's Voxel Space did not use voxels but a heightmap with painter's algorithm.
My personal opinion is that to qualify as 2.5D the game engine must internally use a 3D coordinate system even if the render process is 2D, and 3D requires a true 3D to 3D conversion.