I have seen this short twice and both times I was bowled over by the gorgeous computer-generated animation. Clearly, Pixar is THE studio that sets the animation standard. However, I think this film has a strike against it from the outset and that is because the CARS characters aren't as endearing or timeless as many of the other Pixar creations. They lack the "cuddly factor" or depth of some of the other characters and so, at least to me, it doesn't stack well with the MONSTERS, INC., UP!, RATATOUILLE or INCREDIBLES (among others).
As for the short, it's about Mater and how cowardly he is. The others make up a ghost story and Mater freaks out. It's all great fun for the kids, but adults probably won't love this film unless they are car aficionados or NASCAR fans. To me, it all seemed pretty routine--aside from the great animation.