Some of the things I've gotten good at spotting over the last couple of years are weight and action lines in still images, and weight in movement in animations. 2D animations are more forgiving, because you have the stretch/bounce things to play with. But with so many cartoons moving into the 3D world, there's weight to be considered. You land, and you're going to have knees bending, momentum transferring out, etc. Hair is going to bounce when you nod or jump.
This is something I haven't been able to master in Daz3D, and I haven't begun to work in something more tuned to that kind of thing, but I know what kind of work goes into it; and if it's done right, it pays off.
For example: While LucasFilms had gotten better at fluidity in movement since the Clone Wars 3D movie, you can see here
that the movements themselves are still very flat. There's not much to suggest physics is involved, even stretching it as it's Star Wars.
While the cinematics for League of Legends are much better in the modelling department, I'm looking solely at the physics involved. Within the first minute of this:
you're able to see weight in his movements, as he turns; his weight is shifting from foot to foot, and it's none too steady.
Bioware, in the cinematic trailers for SWTOR, put a lot of attention into the weight of things, and it's evident. If someone gets hit, there's definite reaction, definite movement.
Something I've noticed, though, is that much of the 3D animation coming out now that's not modeled and rendered for live action movies tends to strike a happy balance somewhere just before League of Legends, as far as weight level goes.
Granted, The Clone Wars is, as far as I'm aware, LucasFilm's first 3D venture, but even as a first, it's not impossible to add weight to all the actions. If a character weighs 50 pounds, he/she should move as such. Likewise if they happen to weigh closer to 200. Gravity has an effect on everyone.
Action lines are something entirely different, and all three of these 3D examples pull this off. In art, it's harder to reach action lines, as I've noticed lately in my messages. The concept is simple enough, but it looks like not many people are figuring it out. I've seen some 3D art that held promise, but there weren't anything of what I learned in art class; lines lead the focus toward the intended subject of the image, follow a natural action line so it doesn't look static, use lighting in a way that it's not detracting from the focus, etc.