Why do people keep saying it's just better graphics? If he had a big square design on his chest, and all of the sudden it was a big triangle design with slightly better texture, would that be a graphical update? No that would be a design change, inside of better graphics.
Personally, I'm disappointed in all the aesthetic changes being made in every new Halo installment. You didn't see Darth Vader waltzing around in a new suit every time they came out with a new Star Wars movie or game. You know why? Because he's an icon. Master Chief is just that, but apparently that's about as significant to the developers as maintaining their own canon...