Yeah, Sevendust are nu-metal.
 
I dunno though, there are some worthwhile bands in nu-metal, MuDvAyNe being chief among them.....  

     But ehm, I suppose underground metal has pretty much everything over nu-metal in general; more complexity, better musicianship, often more depth, better lyrical prowess in certain areas.....
 
I reckon it's helpful to think of nu-metal not on the same scale as underground metal, I mean, maybe not to consider it METAL at all (and thereby putting it way down on the relative scale), but rather a completely different form of music. (which i'm sure a lot of people think anyway, but in a totally negative way)   It's more about catchiness and tangible energy, whether aggressive or harmonic....and although those can seem very commercial goals, it still remains that nu-metal has it's own character...plus of course some nu-metal bands 
are depthful and exhibit moods and themes that aren't found in underground metal.  And of course, because it's a different sound, it's a different aesthetic, and you either like some things or you don't, so....
 
One of the things I like about nu-metal is the better aggressive vocals.  While most underground metal growls or grunts or screeches or sings, a lot of good nu-metal just yells or screams, which is (imo) a very effective and tangible method of conveying energy.