This come in from Reddit user CyReN_ who managed to capture a full length game of Spartan Ops which was displayed at this past weekends San Diego Comic Con and upload it to Youtube, Spartan Ops is Halo 4′s Cooperative Mode that replaces Firefight which was featured in Halo 3: ODST and Halo: Reach.
Sit back and enjoy the gameplay, Halo 4 drops 6 November 2012 exclusively for Xbox 360.