If you ask me, the way an image looks, and the testable quality in terms of MTF etc of the lens used are antithetical. The more one introduces a battery of normative tests into lens evaluation, the less one should expect a lens to look "special".
I own two 85mm 1.4 Nikon lenses, the old and the AF-S design. When I went to visit Norman Koren in Boulder some years ago, I took the new one and my D3s, and we ran the lens through Imatest, which Norman probably knows how to use as well as most people on this forum, and as he said it was then the best lens he'd ever tested. It basically outresolved the sensor, edge to edge, mounted on what was at the time a bleeding edge dSLR. And yet, another image geek I know, Iliah Borg, had the same impression as me about the "new lens, if I remember rightly he called it politely "sterile".
Each of the above lenses has its uses, I guess. For repro use or for night photography *against* lights, the new lens with its flat rendering, incredibe sharpness and zero flare is perfect. I actually used it all the time because the images are ok, it focuses super-quickly, and it works perfectly in any context. But if what you want is painterly rendering the old lens is better, and it even has very good sharpness.
People who critique a lens should mention the intended usage to provide context for their opinions.
Edmund
A shoulder doesn't have a blade it has a scapula. Why didn't they call it a shoulder lever since that's what it is? It used to be called a wing bone of all things. Since we don't fly, that was confusing for people too. How we settled on blade is still a mystery since the idea of cutting anything is just as stupid as flying. It's been named as several things such as shovel bone as well. Why the hell don't we just call it a Scapula? We can waste time scoffing at lay terminology or we can just get on with the more important things in our life. 3D, similarly, is a lay term and also an umbrella term because there are a number of distinctly measurable traits that model the dimensionality of an image. Since it's a collection of things, but produces an effect that people can actually recognise, it needs to be given a name so people can argue about it with sock photographers on forum boards.
It's a combination of lens design characteristics, some of which are either neglected through poor design, eliminated for budget, or not important or relevant to the lens designer and/or their market... For some, it's a contribution of design aesthetic. It's considered a luxury in terms of optics and has only gained relevance in design in more recent times. Why does a Ferrari look so much better than a Toyota? There's lots of reason, but mostly because it's more expensive.