Okay, so judging from the gameplay vids that Bungie posted on their YouTube channel, I have deduced a number of things.

1) Countdown is set in the Sabre launch facility...

2) ...and correct me if I'm wrong, but Boardwalk takes place on a yacht, a park, or a boardwalk. Any one of them should suffice.

3) Scripted death animations are in. Similar to how in Bad Company 2, if your character got sniped [online], then sometimes he would clutch his throat. In the boardwalk video, at about 5:23 you can see that the Spartan tumbles backwards. The physics engine isn't good enough to randomly generate death animations like that.

4) A regular Headhunter game is 8:00. This might've been the time limit in the beta, but considering they're changing everything, that might be a new time. I don't remember much from the beta, except my uber t3h l33t cloaking abilities that got me 3-12 in a match.

5) Team SWAT is in (this time on launch). A Team SWAT match is 12:00, and it seems they've rebranded it to simply SWAT. Everyone starts with a DMR and Magnum with unlimited ammo, no shields or motion sensor, and the Sprint ability.