See the full E3 Portal 2 demonstration
You can now see a good chunk of Portal 2 actually being played at the show, including the disgusting fluid physics, the gorgeous ruins of Aperture Science, and your new Companion... thing. Cheers, IGN!
As Tim says in his impressions post, it really does have the artistic impact of a full-blown Valve game. Portal was attractive in its clean visual language, but the art clearly wasn't the focus. Now that it's proved a brain-twisting non-violent puzzle game can have mass appeal, they can go all out on its sequel. So excited now.