I hate music

Strangely enough, metal was what got me into classical. Someone on an old music board I frequented was commenting on my favorite band at the time (Opeth) and said "they're like a poor man's Mahler." So I went and listened to Mahler, loved it, and my obsession with classical properly began (before then I'd only casually listened to it occasionally). 

The association of metal with "devil's music" is really just borne out of ignorance of the genre, and it should be obvious that pretty much every new genre since the dawn of rock has gotten that label by some members of the religious right. Really, metal should be more closely associated with horror movies. The genre's originator, Black Sabbath, got its name from a Boris Karloff horror movie and many of their songs were inspired by horror films, and that tradition continued with many of the bands that came after. Metal didn't really get devil-ly until the dawn of Norwegian Black Metal, and much of that was due to the extremely long and contentious history that Norway has had with Christianity (going all the way back to the vikings). But outside that, metal, including other black/death metal, has covered an immense variety of subjects. 

Personally, I don't hear negativity when I listen to most metal. One thing I like about metal is that it's more "abstract" than most popular genres. By "abstract" I mean that it tends to focus more on basic, purely musical elements like rhythm and structure as opposed to tonal or emotional elements where even the "aggression" just becomes like a surface aspect. To take an extreme example, what Meshuggah does with rhythm (especially polyrhythms) is highly sophisticated, but if all you're listening to is the "screaming" then you'll completely miss it. Really, I'd say what attracts me to many bands is their very unusual (for popular music) approach to song-writing and composition where there's more variety than verse-chorus-verse done all in 4/4 time. For just two examples: 



Now, try to count (or tap your toes/fingers) to the beat on this. Chances are you can't, even though the underlying base meter is 4/4, the riffs (and many beats) are syncopated and cyclical, landing at very unusual points in the meter. There's even a paper online that explains this: societymusictheory.org/files/2014_handouts/capuzzo.pdf

Here's another: 

Try to map the structure of this song. You basically have two different intros before it goes into the main portion, which itself breaks down a few times to do something different, shifting between acoustic/electric and "clean/growl" vocals. You'll never hear a structure like this in contemporary pop music (maybe back in the day when prog was popular). 

For a more traditional, but still sophisticated, take on the genre, try this: 

Even though it's not as overtly complex as the first two, there's still quite a bit going on here, especially with the tempo changes and the virtuosic instrumental prowess (really listen to the drums and the fretless bass work). 

Finally, I'll also add that the association of classical with "heavenly music" is almost as false as the metal/devil music one. There are lots of classical pieces, especially from the late-19th century onward, that are as dark and heavy and most metal. In fact, metal's most basic element--the insistent, pulsating riff--can be heard at least as far back as Stravinsky's Rite of Spring, especially the Danse des adolescents: 



You can also hear it in an even early context in the scherzo of Bruckner's 9th Symphonies (many of his scherzos have metal-ish elements actually):