Actually Mudvayne has frequently been called progressive nu-metal. (*braces for the sure onslaught of flames*) For one thing they can play, and have an interesting use and cycling of time signatures. A trait that grounds them in nu-metal is their guitar riffing, which tends to never go into one note lines a la thrash, settling instead for a chunkier, lower sound. However, this is not just the one massive power chord strike going on. Additionally, they brought the bass back as an actual instrument, not just something to be heavier. Listen to the bass on "Death Blooms" or "Severed" - You can actually hear it, it's interesting, and a has a melodic (sometimes at the forefront) purpose. Additionally, while some of the lyrics are angsty, to my mind they are portrayed much more intelligently, many times with a metaphoric/progressive/concept bent. "Severed" again comes to mind, with a typical familial angst, rebellion theme portrayed as
"I spit up on my plate and then I turn and walk away,
I spit up on my plate and I disrupt the family,
I spit up on my plate as I sever the entity,
And I feel your warm sun on my face
Separate.. Separate.. Separate.. Separate"
Another is the ending of "Death Blooms":
"Dark for fear of failure - an inner gloom as wide as an eye and
fermenting - roiling hate - death grip in my veins - unveiling rancid
petals, flowering forth foul nectar - the space between a blink and a
tear ...death blooms."
This has become slightly off-topic, but the point is that there are good bands who can fit under the nu-metal genre. I'm sure I'll get flamed for liking System of a Down, but if we want to talk progressive, they constantly evolve, add numerous, constantly expanding influences, and are always changing. Their songs follow standard structures many times, but the nature of "progressive" does not automatically dictate what must progress or evolve from the "normal". And I don't think you need 10 min. songs to be progressive.
Anyway, my point is nu-metal gets a lot of shit, and a lot of it is deserved. But there are a lot of fucking dumbass "true" or "real" metal fans whose heads are just as far up their asses as the typical nu-metal fan, especially with the whole "unless only me and my friend are the only people who know this band and we constantly masturbate each other and swim in the pool of our frolicky, underground-only-loving semen while listening to this crappy, sub-demo quality 'album', then the band is a sellout". Anyway, Cheers!