So much of Halo 4, like the rest of the series, is busy. Lots of action, lots of colours, lots of stuff all over the screen. So this concept art from the game is a refreshing break, stripping things back to let us see the game's enemies and locations on nothing but a field of white.
I particularly like the shots of the game's villain, the Didact, as he's just a bunch of sketches, testing stuff out like what he's going to look like, and how all that fancy transforming armour is actually going to transform. I also like the Grunt with his mask off, where he looks even more like the slapstick opponent he normally is.
Most interesting, though, is the image of Cortana above. For a character whose appearance had been largely nailed down in previous games, the thought of her going all Helena Bonham Carter in Halo 4 is one I'd have liked to see the developers run with. Especially since it kinda fits with the story!
If you want to see these at a larger, more tangible size, they're all available in the game's official art book, which like the recent Assassin's Creed III book marks a return to big games getting books just about their art, instead of including it alongside a bunch of other stuff you don't buy coffee table books for.
To see the larger pics in all their glory (or, if they're big enough, so you can save them as wallpaper), right-click on them below and select "open in new tab".