Linkin Park and Disturbed both came out about the time I was finishing high school. I knew something was wrong, very quickly.
I was a big fan of grunge music at the time. Why I could not accept them is a bit of a mystery, and I think I am a bit inconsistent about it too, to be completely honest. What I have against them I can only describe by means of a metaphor: They are that kid in high school that gets expelled, or breaks his nose, or cuts his arm, and then shows it off to you saying "Look how fucked up I am."
I just cannot stand that attitude. To take it a bit further, please excuse the use of Baudrillard. I think that the grunge guys were depressed by life and expressed that in their music. The nu-metal guys learned how to look and sound depressed by watching grunge and metal videos. There always seemed to be something cheap and shallow in their self loathing.
Oh, and that image. Gelled and dyed spiky hair and trackpants. Disgusting! I just cannot stand that manufactured image. I will admit that there is some of that in grunge as well, particularly on Pearl Jam's Ten; but for the most part, they just dressed like regular people. Kurt Cobain at the end was a bad example: I think he went to the pawn shop and just grabbed anything- I don't like it when he does it either.
For what it is worth, LP, Disturbed and Korn seem to have improved in later years. Occasionally, I hear later songs and they sound ok, but I never listen to it.