I saw an article that broke down the clip. The most obvious things are as follows: The coolness of the shield (how sweet was that?), the assault rifle is back (yay!), the REAL pistol is back! (look at the tale-tale screw on the back of the gun), Master Chief does indeed sprint and might be able to do so in-game, the Mongoose ATV is in, the Brutes look nasty and one has a Warhammer (they have already stated that there will be new combos with weapons so is it hammer time?).
I do think they will use the boy as a young Chief. Hey, it's better than a giant plant (as pointed out by someone). I hope they stay away from playing as the covenant