"Et tu brute?" Video Documentary

The ViDoc explains that the three classes of Brutes have been differentiated, the same way Halo: Combat Evolved and Halo 2 featured different classes of Elites, Grunts, and Jackals. They are all shown with much heavier armor than the Brutes in Halo 2:[18]
'Standard' infantry Brutes that wear blue armor held together by buckles. Brute Captains, who wear more elaborate helmets and armor. Brute Chieftains, who have the most elaborate helmets and armor. The color scheme of Elites in the prior games seems to have been applied to Brutes (blue is the lowest rank, red is higher, and gold is the highest). To reflect the Brutes' violent nature, more violent animations have been created. Examples shown in the ViDoc include a Brute ripping off the arms of a Marine, a Brute ramming a Marine into a vehicle, and another Brute punching the stomach of a Marine lying on the ground.
The AI has also been updated to incorporate the new idea of a Brute pack. A Chieftain in Halo 3 may order all of its troops to throw grenades at the enemy together, or may decide to focus on attacking one character.[18]
The film also includes some other previously unseen elements, such as dual-wieldable Energy Swords (only used by AI) and the new Spike Grenade.[19] The "Spike Grenades" may stick to any surface except water and release a shaped charge upon explosion. A Brute Chieftain is seen firing a weapon resembling an un-deployed plasma turret from Halo 2. However, the game as shown, is still in a pre-alpha stage, and the graphics and game elements in the ViDoc are currently unconfirmed for final release in the game.