Aside from color and translucency, an original artwork shows also the relief. It can tell much about the creation process of a painting and adds additional texture.
Furthermore, some pigments were expensive and hard to work with prior to the 19th century such that artists used it very sparingly.
This stood out to me the very first time I saw Starry Night at MoMa. The paint is so thickly layered, and you can see the individual brush strokes in stark relief.
It makes me wish for a VR app with ultra HD reproductions, you could have normal maps and other 3d techniques to add another level of fidelity, the scale is also not a problem in VR.
