For all the people making snide remarks on the cloak, here are 2 possible reasons for it, just off the top of my head:
1.Protect the armor. Sand getting in joints could cause problems over time, and when they show the helmet you can see it's already suffered a lot of wear and tear which would be compounded, again over time, by sand and high winds. I don't think the armor's shields would protect him against the sand unless the particles are moving at high enough speeds to cause instant significant damage (think space dust moving at hundreds of meters per second), or it's possible his shields aren't working in the cutscene.
2.Inhibit long-range identification. The cloak breaks up the outline enough that anyone observing from a distance wouldn't think "Mjolnir armor". Additionally it looks like it might be thick enough to at least alter his heat signature.
As for the game itself... I'm invested enough in the Halo story that I would very much like to play this game when it comes out, however for me to go out and actually buy an Xbox One, given what we know about it so far, the storyline of the game would have to be so good that it wins the Nobel Prize in Literature.