I was gifted a copy of Mistborn by Sanderson and I've been having trouble reading. The first handful of chapters dragged for me, so I put it down in favor or something else. I think you point about flat characters is what did it for me; I believe good characters can carry a mediocre story, but a story has to be really exceptional to carry a narrative with uninteresting characters.

I am hoping to give it another shot this summer, but I can't exactly say I am looking forward to it.