Honestly, I imagined that Master Chief would look kind of like the guy who voice him (Steve Downes) Not just because he IS MC's voice- but because he's an older guy and looks, well... just kind of average, like any guy and I always thought of that about Master Chief, a guy who's basically known for the ass he kicks and nothing else, but nothing particularly special about him besides the fact that he's REALLY good at kicking ass.
Plus, Steve Downes makes a mean chili