I really love the new trailer, especially the music, and seem to watch it everytime I go on my Xbox 360 dashboard. Since I've seen it quite a lot now I've picked up on quite a few things in the trailer.
1. The girl in the blue armour (I think her accent was Russian) has a bionic right arm with a few armour plates attached,
2. The Spartan who says "Didn't think anyone survived Pegasi, sir" is George-052.
3. The 'commander' is Carter-259. If you remember there were only 150 Spartans considered for the Spartan II program in the books, so he is unlikely to be from the same group as John and the rest. He also isn't a Spartan III as '259' would put him in Alpha batch, and they were all killed during their mission, not to mention the fact he's too tall for an SIII and wearing the wrong armour. It is possible he is from a second batch of SIIs as in the books it said after training the first lot of SIIs CPO Mendez was reassigned to train the next class.
4. The girl in the blue armour is numbered 320 (I can't read her name), which again would put her in a different class to the Spartans we know from the books. It is possible from her number that the selection pool was widened to 200 otherwise her number would be below 300.
5. Carter liekly has the title commander due to being mission commander of that group of Spartans. John-117 had the highest rank (of the known surviving Spartans) at Master Chief Petty Officer, until Kurt-051 gave a field promotion to Fred-104 during the events on Onyx, which means no Spartans held oficer ranks during the Human-Covenant war (2525 - 2552).
6. Due to the previous point, it means that the 'Lieutenant' is not likely a Spartan, even if he is as tall as them (then again, there are some people who grow to be very tall), unless Bungie are breaking from canon and making some of the second class of SIIs officers.
7. None of the Spartans are wearing the MJOLNIR Mk.V armour worn by John-117 and most other Spartans during the conflict on Reach. Its possible this is a specialist group seperated from the others, or already stationed on Reach purposed for another mission.
8. One of the Spartans has the EVA armour variant (which did exist at the time) and has a very distinct skull-type pattern painted on their helmet. No name or number are visible to me in the trailer.
9. The Spartan withthe sniper rifle on the new aircraft (not a Hornet as in Halo Wars they were more-or-less the same as in Halo 3) says "This our new number 6", showing that it's a 6-man team, and the posibility of 6-player co-op.
10. Carter mentions that the 'lieutenants' file had parts that ONI didn't want anyone to read. Although all Spartans were part of ONI Section 3 (NavSpecWar), there were other units operating in ONI. It is also possible that he is from another unit, like the Marine Corps, and has simply taken part in classified operations.