Voice commands seem to be a more robust option than previously thought. As well as switching graphical modes, players can shout "Reload Weapon" to reload and "Grenade!" to, you guessed it, throw a grenade.
Perhaps more interesting is the Library feature. Players can approach items, characters and enemies in the environment and say "Analyse" which will capture a 3D model of the item as well as descriptive details for an encyclopedia that the player can look through.
A video showcasing the details should be available soon, with a more robust look at the new features hitting Halo Waypoint this Monday.