New trailer
Make sure to watch it HD
You can see Valve really want to show off the engine; you get to see companion cubes and turrets being constructed from scratch ^_^ And the lighting enhancements are made much more obvious, too.
Portal 2 video: Stephen Merchant debuts as Wheatley | Joystiq
Also, wootness at a non-villain British voice actor ^_^ Well, presumably non-villain.