You should expect everything!
It's a little scary at first how big it is, the 10 minute walk, the number of people in the stands. But it's just like 3 days of constant energy. And it's amazing the kinds of people you can meet there.
Oh and there's a rockin party on Saturday night hosted by FIRST. It makes the team socials from regional events look so sad...
One thing that is different from some regionals is that because the dome is so far from the pits if you're spending most of your day in the stands scouting matches/cheering you probably won't see your drive team or pit crew much at all during the day.