Check out this wicked video by 343 that gives an insider's viewpoint on what Halo 4's multiplayer has to offer. It's full of Infinity, the Mantis, designer commment, ranking and Forge mode. It's comparable to the Vidocs that Bungie used to do to promote their Halo games.
Oh and did I mention the music that plays near the end of the vidoc? It's just magical.