First off, Halo Channel was announced, which will provide gamers on Xbox One with a central hub for all their Halo-related gaming needs. In many ways, it looks like the natural evolution of Halo Waypoint, which first launched back on Xbox 360.
In addition, the studio announced another Halo 2 map remake for Halo: The Master Chief Collection, that being the fan favorite, Sanctuary. On top of that, the 343i also detailed the game's online multiplayer ranking system, confirming that Halo 2's skill-based system will serve as the foundation for how The Master Chief Collection will rank players.
Halo 5: Guardians also got a little love, as 343 Industries spoke a bit about the upcoming multiplayer beta. It will include a handful of different maps all built around 4v4 arena combat.