I love these - so expressive while being INCREDIBLY line efficient. Simple is best!
In particular, I love her hair. I always have a really hard time drawing hair. But on any given person, their hair tends to clump together into fairly distinct forms, and the artist simplifies the process by just drawing the outlines of these clumps. At a glance, you can tell exactly what her hair is doing, and it lends movement to the image. For example, in the sketch at the top left of the above image, the way the ends of her hair fan out tell you that she has just spun her head around to look in our direction. In the bottom left sketch, you can tell she has just leaned forward by the way her hair has partially slipped over her shoulder, but the rest is still being held back.
These things sound like no-brainers, but it's little stuff like this that brings a drawing to life.
I also love that it's in black and white. Sometimes I struggle with getting my sketches to read without using color. But these last few frames are instantly understandable. And also beautiful! Basically, I'm more excited for this short than I am for Wreck-It Ralph (although I'm really excited about that too... way more excited than any self-respecting 20-something should be).
UPDATE 1/31/13: Disney Animation has posted the full short online!! Watch here: