It looks like it's going to be all linear and stuff.
And Elijah seems like a total badass, I hope I can make him elder again.
Most DLC for the Fallout Series was if I'm not mistaken. Broken Steel was fairly linear (you COULD go and do something else for a bit but once you got into the main mission that was that), as was Operation: Anchorage (I think it was called) and Mothership Zeta. The Pitt I never heard anything about or played so I don't know its deal, I know that the other one wasn't... but yeah, the idea is that the DLC generally gives you a 3 - 5 hour story with a couple extra side quests at the end to do.
As for the trailer, I wasn't really expecting anything this cool. I kind of figured it'd be "take a long walk to a Casino, fight some people in a Casino (or robots), go steal the treasure, yay." This looks pretty interesting, though I know that if I have the option, I'm killing the person who put the slave collar around my neck when I'm done.