In a recent series of tweets, ex Halo developer Marcus Lehto had a ton of things to say regarding the history of the Halo franchise, his feelings on 343's games, and his opinions about what may be happening with the upcoming Halo Infinite. One particular tweet described Master Chief's face - something that's only been briefly teased before in the legendary ending of Halo 4.
Lehto described Master Chief's face as "heroic but also kinda brutal," giving fans a general description to go off of. He mentions early sketches of John that portray him as bald, and covered in scars. The description checks out with the teased image from Halo 4, and fits the lore pretty well. Years of heavy combat experience leaves its marks, after all - not to mention heavy genetic modification.
We had a very early sketch of John 117 that had him bald from years of wearing a helmet and scars over most of his exposed skin. He was heroic but also kinda brutal at the same time.— Marcus Lehto (@game_fabricator) September 15, 2018
It's entirely possible fans may be able to get a full look at John's face in Halo Infinite, although it isn't likely. The Chief's face seems to have entered the pantheon of great secrets in popular gaming, becoming one of those things that fans of the franchise very much enjoy having their own theories about.
The Halo franchise got its first - and really only - clear look at John's face in the Fall of Reach miniseries. This adaptation of the novel of the same name covers the history of the Spartan program and shows off a younger version of Master Chief as he goes through his training. The appearance of a combat-worn, adult John would, of course, be significantly different, however.
Other highlights of Lehto's tweets include comments on Halo 4, where he noted that Bungie would have taken the game in a "very different direction." He also made note of some old vehicles that were meant to be in Halo: Combat Evolved, along with cut features like water combat and squad commands.