1 - A broad genre that consists of great bands and shitty bands. Self proclaimed "true" metal-heads who listen to only speed metal or thrash metal and think that all the metal world has to offer is fast guitar riffs in straight E tuning and lyrics that were written in an instant and the same damn solo in every song that was pretty amazing the first time you heard it until you realized it was just some guy playing some scale really fast and then jerking the fuck off his whammy bar without any emotion whatsoever. These "true" metal-heads denounce Nu Metal because of its lack of guitar solos and say it's unemotional fast guitar riffs in low dropped tuning and their singers don't sing. So basically the difference is that the two forms of metal are in two different tunings and one of them doesn't consist of solos and makes up for that with emotion.
2-Too broad a term to really paint a picture of but is characterized by electronics, emotion, a tendancy to piss off a hypocritical self (and wrongly) proclaimed "true" metalhead (who should listen to some fucking Tool and Alice in Chains if he wants to know which talented bands to compare nu metal bands to in order to show how untalented they are), and less talent than the metal of the late 80s and early 90s. Sure nu metal bands lack solos and tend to write most of their songs in the same key and don't do anything that's technically amazing, but they have more emotion than all every "true" metalhead's bands combined! The downside to Nu Metal
3-Unfortunately a genre that appeals to teenagers who think they're depressed but are just too dumb to look around themselves and see that everyone else is going through the same thing, really haven't heard any real real real music and listen to bands because of the lyrics that are simple and dark enough for them to relate to and the image of the band. It's because of these dumbasses that everyone else hates nu metal.
You really have to be open minded (or dumb enough to think you're depressed because you're a normal teenager) to listen to Nu Metal
Sure, Nu Metal bands aren't nearly as talented as 90's metal bands, but they're a helluva lot more emotional and interesting than emo and screamo bands