It is not really any more 3D than the Saturn as it still does texture mapping in 2D space, same as the saturn. It's biggest advantage when it came to 3D graphics, aside from higher performance, was it's UV mapping. They both stretch flat 2D textured shapes around to fake 3D.

The N64 is really far beyond the other two in terms of being "fully 3D", with it's fully perspective correct z buffering and texture mapping, let alone mipmapping with bilinear blending and subpixel correct rasterization.