Damn, people fell for what Killer said.
Anyways, the Valve team have always loved to make entirely new animations. They hardly reuse previous game animations, and try to adopt hundreds to thousands of little animations that most people won't pay attention to. I enjoy seeing new animations, especially the left4dead series where zombies will fall and stagger back to their feet. Their previous series never had that, so you can see the large amount of detail they try to enhance each new game with.
With Portal 2, I hope to see all the new features.