This particular thread is one of the more useful discussions on the aesthetic trends in 40K that I've seen in a while, going beyond level of detail, phwoar factor and producer ranking. It's at BoLS believe it or not, on a more or less ephemeral post.
One of the arguments corresponds to that idea that D&D is now its own set of reference points, which came up again with the nods to past fiction in fifth edition. A couple more:
Technical precision and intricate detail are nice, but those old minis had attitude; they projected a mood and a tone that permeated the entire range and let you know exactly what kind of game you were playing.
Patrick at False Machine has some related questions, and especially nos. 2, 4, 5, 15 and 16, but they're all worth a mull, not least for actually having been formed and asked.
It is possible that a combination of the limited means of lead casting and the, kind of, artistic 'moment' of the times meant that early citadel miniatures were better sculptures in this way. Less perfect as pictured things, and maybe not as skilled. But they occupied space and held mass in a different way and in that sense, were more pure sculptures because they did that thing that only sculpture can do.
And they were made of lead, which weighs differently in the hand. And people might say why does it matter if the shape is better and I would reply why wouldn't it. It is a tactile form. it is a haptic form. The weight is part of what it is. It's not just what the material can do it is also what the material is.
If you want a sense of the truth of that, and from scratch, you could try Oldhammer, and orlygg's posts on the older 'Eavy Metal pages are a quick, cheap start, if less interactive.
Personally, I think it's also about assembly, and the range of options in a kit. I think we could propose a simple rule: all else being equal, the more poseable a miniature, the more formless any given finished effect, and maybe the more gormless in appearance. That last could be a death knell for the so-called 'angels of death', and fellow hard-cases.
Why? Because scope for poseability implies leftover freedom, space that to a degree someone other than the sculptor has to mitigate. This pragmatic blend in the name of choice conveys a less pure vision. If everything is possible, does anything carry weight?
Unlike Parmenides, Beethoven apparently viewed weight as something positive. Since the German word schwer means both 'difficult' and 'heavy', Beethoven's 'difficult resolution' may be construed as a 'heavy' or 'weighty resolution'. The weighty resolution is at one with the voice of Fate ('Es muss sein!'); necessity, weight, and value are three concepts inextricably bound: only necessity is heavy, and only what is heavy has value.
This is a conviction born of Beethoven's music, and although we cannot ignore the possibility (or even probability) that it owes its origins more to Beethoven's commentators than to Beethoven himself, we all more or less share it: we believe that the greatness of man stems from the fact that he bears his fate as Atlas bore the heavens on his shoulders.
We may be wrong. But any such belief would be presumably be key to an appreciation of the aesthetics of a grim, dark future of burdened humankind. A slow counteraction or nullification of the grimdark with this kind of lightness could be crucial to any decline in the aesthetics of 40K, and possibly, with the change in materials and kits in the past 20 years or so, and maybe the rapid releases in the past couple, also to a decline for GW._