I am an avid comic reader, with nearly complete collections of multiple comics. That being said, White Sands was comparably a let down. SPOILERS:
Skaa has said it best. The biggest drawback for me was the pacing. Sanderson writes novels. (Yes he writes short stories as well, but White Sands is not one of them) These novels have large amounts of world building and take a couple hundred pages to keep the smooth transitions of characters and plot flowing in the cohesive and action-packed stories that Sanderson is amazing at.
Unfortunately this graphic novel seemed jarring as it attempted to draw the world, showcase the action, keep the plot moving, and make us care about the characters. SPOILER: At one point Kenton is amazed at another characters use of a pistol. Yet the next page it's admitted that the Sand Masters lifelong enemies use something "Extremely similar". So why the shock and awe?
End of the day: My take is it would have been much better served as just a true novel or with more pages of graphics and dialogue to help it flow.
*Edit* Also as everyone else seems to have mentioned, the Sand Master clones... come on man, I bought the hardback and I still had to squint at um to see differences.