Completely out of left field we get footage from a vastly polished version of the demo being played at G-Star. I'll point out what new stuff I managed to notice for each segment (I don't know that they're entirely in order). Keep in mind that the video quality isn't great.
EDIT: Now noticed that the player had a full bar of weapon skills by the end of the tutorial, which indicates lower unlock requirements. The map has a legend now, which seems like an obvious step forward. And of course the entire personal story sequence at the end with the bandit disguise is new. Hopefully that's a representation of the sort of mission variation we'll get based on our biography choices (for reference, this character is a street rat).
I can't see any of the content or systems changes that ArenaNet has been talking about recently, but everything here just has an extra, much-appreciated layer of spit-shine on it. That in itself seems insane given how much praise has been heaped onto previous versions of the demo for their "AAA" levels of polish.
If you're astute enough to catch any alterations or improvements that I haven't, make sure to point them out below.