Well, I don't have an art degree. As a practical example, if you gave me two different dishes of food and I said I prefer one over the other, do I need to be able to tell in what exact way I liked it better for it to be true? I might not understand what seasoning you used or how you cooked it - some things you just like innately, and I could try to go out of my way to explain it and do a poor job of it.
But since you asked, and I am assuming these are good faith questions, I'll try to regardless:
1 - By something like this, I mean a graphical update, new shading, textures, models, etc.
2 - Nothing bothered me, but by the same token I was unsatisfied. Especially when it comes to the way the shadows affect the face and how it looks, how the light reflected poorly in certain cases, on how darker-skinned characters didn't have a skin that looked as natural in certain lighting environments (especially in darker areas).
3 - I didn't first hear of it until they actually showcased it, so I guess I didn't have any expectations. I was positively surprised when I saw it!
4 - See 3. But yes, very satisfied, it looked better in-game (creator and benchmark) than I expected (I especially love how the light shines through the ears and their new textures, and how they softened a lot of the more "jagged" facial features (which really just screamed low poly)).
Again, I'm no 3d artist.
I like the changes across the board. Every character looks a bit different, but then so do people's faces in the real world as they grow and age and so for me that really isn't a huge deal. I empathize with people who do, I just happen to disagree with them on what's important.
I'll take slight changes to my character over time if it means an improved experience, over it staying the same for the sake of comfort.
Lastly, I wouldn't mind at all if they added the new models as just separate choices and allowed people to stick to the old ones if they prefer. That would satisfy both camps, and I'd support that far and above the idea of them going back altogether.