I'm not one to flame, and this is just my opinion, but I've always found bands like Disturbed, Deftones, Drowning Pool, and the like to all be incredibly whiney, cliche, and contradictory.
For one thing, all of the bands seem to essentially convey the same two messages. "Why don't you like me", "I'm different from everybody else and I don't care," and "I have a very horrible life."
My first complaint is, if they don't care what anyone thinks, then why do they complain when people don't like them? Chaindog's quote of Slipknot saying "You keep mocking me!" is a good example of this.
Second, the definition of different is, "Unique in form, quality, amount, or nature; Distinct or separate." That being the case, how is it that the untrained eye can look at a fan of nu-metal and instantly identify them as such? If one were truely unique, it would be nearly impossible to identify what sort of music they liked.
Third, many of the band members in these bands grew up in middle-, if not upper-class, homes. Granted, some of them have divorced parents, dead family members, and what have you. However, I fail to see how that makes their lives so horrible in comparison to every other American that they should dedicate entire albums to their plight. Along with that, many of these bands have gotten very rich from their first albums - rich to a point that you and I could only imagine. Therefore, why do they release yet another album complaining about their horrible lives? I fail to see the horrible life of a man who is insanely rich, has many males who wish they were him, and many females who wish they were dating him.
Finally, a counter to Chaindog's comment about Slipknot.
Slipknot is revolutionary in the metal world. They have quick paced lyrics. Heavy screaming fits. And then in mid song they switch style and have a slowly lyrical spot.
I hate to say this, but there is simply nothing revolutionary about that. Not in metal, and certainly not in music in general. Black Sabbath, which released it's first album in 1970, was doing what you describe 30 years prior. Elvis Presley was doing it before that.
For more recent examples, Theater of Tragedy recorded their first album in 1995, and they, too, had fast-paced lyrics, screeching, and mid-song switches to melodic sounds and singing. And on top of that, their lyrics were slightly more meaningful than "Pentex sucks! Pentex sucks! They drain the life force of my tribe! Pentex sucks!"