In the video they'll show off the 3rd level in the campaign along with a trailer for Forward Unto Dawn as well as an appearance from Master Chief bringing in the Halo 4 console. He mentions that there will be 4 player co-op and that the other players will be spartans.
Also were revealed some screen shots of which CVG reports the return of THE FLOOD in a new multiplayer mode that supports up to 10 players. If you've played multiplayer on Halo before you might remember a mode called infection. This is the generally infection but I'm gussing you'll respawn as the flood and as you can see in the picture below it looks as if the claw would act as the sword would have from infection.