The last episode of Forward Unto Dawn (there are five in all) has been released. The live-action mini series covers events that lead up to the imminent game, and so it's the perfect way in which to prepare for the release of Halo 4 next week (that, and a few games of Halo: Reach).
The fifth episode has been posted on Halo Waypoint. For more details on 343's effort you can check out our Essentials article, alternatively, our Halo 4 review can be found here.