One of the folks at 343 posted a link to these.
As a person who absolutely loves viewing concept art, I had to repost these here.

Description by “Shae” of 343:

Spartan Ops: Apex

HALO 4 Spartan Ops pre-production paintings. Early on, we were seeking to create a mini-narrative that would make for a compelling multi-session based experience, where players could take over an outpost one week, fly a pelican mission the next week and fight their way up a hillside where they could infiltrate a forerunner technology compound. The paintings that follow were the result of various collaborations with BJ Christian, Nicolas Bouvier, Kenneth Scott. This level went on to become as “Apex.”

Source Link: http://shaeshatz.blogspot.com/2013/02/apex.html

Such rich and wonderful colors. I can’t help but appreciate this as an artist myself.