The full moon cowered behind the jagged peaks of the Aros mountains. It watched as three men entered the dark stone walls of Gasa Vitoli. It hid its face from them and hoped that the monolithic shadows it cast across the plain might cause them to stumble and turn back, to abandon their mission and restore hope, but the three men continued onwards.
Three men brought together to pull off one heist, but each driven by a different motive.
Althus, the grizzled veteran, was driven by duty,
Nelson, the scabrous ruffian, was driven by greed,
but Ian, the unassuming mage, was driven by a loftier desire; The desire to save the world.
 

This kind of stumped me:

It hid its face from them and hoped that the monolithic shadows it cast across the plain might cause them to stumble and turn back, to abandon their mission and restore hope, but the three men continued onwards.

Nice imagery, but what the heck do you mean by "...to abandon their mission and restore hope..." ?? Do you mean that by abandoning their mission hope will be restored? A little unclear, at least to my muddled mind.

Is the moon a character or is it only personified in the opening paragraph?

This beginning is a little distant from the characters (not that that is bad; I think it works), but it gives the feel of a fairy tale or a folktale, at least to me. Is that what you intended?
 

As for the anthropomorphization of the moon, its just a literary method. Again, I think the wording could be tweaked a little to ensure the right idea is being conveyed.