Even more than the fact that he became the villain, that's why I'm against him, and have been for some time. Even if he attempts some form of redemption in the final two episodes, he's gone too far. He's certainly the most interesting character, as ADG says, but he's caused too much damage for selfish reasons.

Right from the very start where he turned down a friend's charity in favor of making meth, Walt has put his pride first in every situation. Even in the instances where he's forced to do something bad for his own self-preservation, he could have avoided the situation entirely if he'd just let go of his pride at some earlier junction. But every step of the way he refused to either back down or accept good enough as good enough. He has killed people, watched people die, covered up murders, and ordered the murder of others. He went too far, and when he finally tried to stop, it was too late.

Now, yeah, he's being punished for it, and he deserves to be. But that's not what matters. What matters is how much damage he's done to those around him. Hank is dead, his family is in tatters and Skyler will probably end up in prison when everything comes out. Todd and his uncle's gang might come for Marie, since Jesse told them that she has the taped confession, and those guys would not hesitate to hurt her. Gus was not a good guy, but he ran a clean operation and when Walt killed him (the end game of a series of events that started because of Walt's pride and paranoia), it opened the doors for people like Todd's uncle. Jesse was a loser, but he always had hidden potential and Walt has destroyed his life. The world would be a better place if someone had turned on Walt a long time ago.

So I'm not cheering for Walt. I don't feel sorry for him at all. I'll be fine if he attempts some sort of redemption, but he's already done too much harm to earn forgiveness.