It isn't just Mat, its the entire book. Here's a quick breakdown:
1) Every character is the same. Its true and you know it. Tuon's lines are indistinguishable from Avienda, Min, Mat, Rand, -- everyone is the same. I have to wonder whether Sanderson ever even considered that these are DIFFERENT PEOPLE. It is literally the same person each time with a different name.
2) The writer. He 'broke the immersion' way more than the absurd dialogue. Its as if the Reader is attempting to be in Randland, but there is a huge, thick pane of Sticky-Sanderson-Glass in the way. You may get the occasional uninterrupted glimpse of what's going on, but for the most part you're sitting there struggling to see anything at all.
I hate to be the first real negative reviewer, but this has been a huge disappointment, especially after the positive reviews I saw on this site before reading the book. I kept wondering, how in the world did they miss this? I even suspected TOR of paying people off! TGS is almost on the level of some junk fantasy novel, like Eragon or Twilight. I just don't understand why no one has spoken up about this yet. The last 11 books are the only things that could ever make it worth your time. What a waste.