Eww, at Dillinger Escape Plan and Norma Jean imo. But I couldn't agree more that metal bands pigeon-hole themselves into being generic. I definitely think you should check out Spiral Architect and Anacrusis though, you'd probably enjoy them, they are two of the few bands I respect for originality.
Nu-metal is hardly even a sub-genre. It's a place people shove bands that don't qualify into other sub-genres. Korn has little in common with System of a Down or Slipknot, but there they are being blanketed as nu-metal. Life is Peachy is one of the most original albums there are. I'm not a huge fan of Korn, but they were original. That said, after the first few albums they failed to really develop or expand.
Opeth is definitely a rock band at times. Undeniably on the Damnation album. They don't let them pigeon-hole themselves and I respect that.