In an E3 interview with Official Xbox Magazine, O'Connor, formerly of Bungie and the Halo series' Franchise Director, had this to say: "There's some story behind his new look... There are specific reasons why he looks the way he does and why some of his behaviours have changed. We'll see in good time."
That means changes to his personality as well as just the armour, then. Intriguing.
Some of us noticed the changes to Master Chief's Spartan armour in the E3 reveal trailer – in particular, the gap in the armour around the groin that was previously covered by a shiny green metal plate.
Bye-bye, Spartan codpiece! We will all miss you.