Nu vs. Underground(IMO):
I listen to the radio a fair amount in the morning, Phoenix has one of the better hard rock stations I've heard...but now it's mostly nu stuff. So I will compare Linkin Park, Nickelback, Lost Prophets, Hoobastank, 3 Days Grace, Seether, and so on to the underground metal that I like(which is far less than most here I admit). I've heard all these bands hits, and some full albums...so I don't immediately dismiss them without knowledge of their sound/style. And there are some bands in the mainstream arena that I do like, although I may not buy much from them...Tool, SoaD, Megadeth...etc.
But the basic nu/mainstream stuff that's out there is very boring and as the original poster says, not deep. It frankly all sounds the same...even bands that I originally liked to a degree like say Godsmack and Disturbed have regurgitated the same song over and over. So IMO they don't begin to approach the creativity, originality and talent of bands such as Opeth, PT, Woods of Ypres, Fates Warning, etc...
The problem with trying to get other people to like the music we do is that they many times are not "music people". They like catchy 3 minute songs that they've heard a million times so they can sing along, that don't take any effort to understand. Try and get someone like that to listen to a 16 minute song and they can't even comprehend...too much work. People who like progressive music(whether mellow or melodeath) are willing to take the time to hear everything going on, hear the subtle parts, understand the stories and so on.
Then you have Slayer and some of the classic metal greats and some may not want to try anything "old" great or not. As far as metalcore, I'm not a big fan really...I do like a few Slipknot songs, but not the entire albums that I've heard. Some of the others I've heard like Lamb of God and Shadows Fall don't do it for me because the vocals are far to repetetive making all the songs sound the same. Overall metalcore seems to suffer from that for me...so I don't understand the popularity and the fact that someone who likes that wouldn't give other metal styles a better chance. Must go back to the prior analysis for them too.
I've tried to turn many onto the prog bands I like, a few took to it...but only because they were prog fans already to a degree. Most aren't really interested and it's sad...but you can't change a persons musical taste completely.
Seth