Last night on AOTS they were playing the beta. They said that journalists have been playing the beta since late last week.
It looked pretty cool. The only weapon that I saw from Halo CE was the AR. The weapons I saw from Halo 2 was the BR, sniper rifle, carbine, and the SMG. All of the weapons from Halo CE and Halo 2 pretty much look the same, they just made the small changes to the way that they look. You can have 4 portable things they said which were the bubble shield, trip mine, personal lift thing, and a power drainer. You can go up to a turret and take it and pack it with you and it will go into a 3rd person camera kind of like GOW. Kevin said they were 7 new weapons avaliable for the beta. Some of the 7 new weapons were the pod missle thing, spartan laser and I think something else, but I cant remember. He was also driving an ATV type vehicle.
If anyone has any questions about the beta I can try to answer them the best I can based on what I saw on AOTS.