My opinion on Mat has really gone down since the middld of The Great Hunt or so. He's gone from one of the good guys, to a neutral guy, and seems to be heading in the wrong direction still.
Mat is SEVERELY lacking in loyalty, and to say I find the extremely disappointing would be an understatement. After everything Rand did for him, everything he risked for Mat, to have Mat ready to throw away a lifelong friendship at the first sign of trouble with Rand is just so disheartening.
He had the nerve to compare Rand channeling with someone torturing small animals, which is just so inaccurate a comparison it's hard to understand. Harming small animals in the way the comparison suggested would be a CHOICE; something by definition done with intention. Rand did not choose to channel, and would stop if he knew how, if he had any idea how to control it.
The more I learn of Mat's character, the less I like him. Aside from clearly having no loyalty, he also has shown little sign of empathizing with others. He has little regard for rules, and doesn't seem to spend much time considering right or wrong. He appears to care about his own well-being over anything else, and most concerning of all, has show signs of being strongly drawn to riches and to a lesser degree glory.
All if this make Mat a prime target for recruitment to the darkness. There is foreshadowing of him betraying Rand, with him telling Rand after the portal stone the he would never betray him, suggesting that in many of the lives he saw, he DID betray Rand.
When you take this with some of the other context from the books so far, it suggests that betrayal could be central to this story. After all, the PROLOGUE to the very first book in the series focused almost entirely on betrayal. The way Ishmael was speaking to Lews Therin strongly suggested that they had long known each other. He literally called himself the Betrayer of Hope. And while the name undoubtedly refers to hope for the world at large, I also seem to remember something about the Dragon being the hope of the light, and of the world, which suggests the Ishmael may have been a frined, or someone Lews Therin trusted, whose defection to darkness represented a personal betrayal.
He then forced Lews Therin to understand that he had unwittingly become a betrayer, too, by becoming the Kinslayer and killing everyone he had ever loved, and everyone who had ever loved him.
Most of all, is the theme that comes up again and again, of the pattern, and stories, people, and relationships repeating lifetime after lifetime.
Right now, there is no reason to think that Ishmael is not still locked up in Shayol Ghul, likely not far from the Dark One himself, since the Betrayer of Hope is said to have been the leader and most powerful of the forsaken. So it doesn't seem likely that Mat is the reborn Ishmael, and yet I still get the feeling that he is being put on the road to betray Rand, and join the darkness.
I wish I could end on a more cheerful note, but things are almost certainly going to get worse, before things can get better.