I think Sanderson himself would agree that his writing is not meant to be considered serious literature. No fantasy or sci-fi writer alive today, other than Goodkind (who is perhaps one of the worst writers alive), has actually tried to claim that their books are meant to be serious literature.

Generally, storytelling is only one facet of good literature. Style, pacing, tone, meaning and significance are all important when we talk about a book as an artistic achievement.

Sanderson's stories are very entertaining, but his style definitely needs work. There are tired cliches in his writing, overdescription, awkward sentences, etc. I don't happen to care about the style as much (which is getting better, in all fairness) because I don't judge his books by the same standard that I would judge, say, Dickens or Dostoevsky. It does grate on some people, though, and I think it's a valid criticism to make.