Mahler's 6th Symphony was metal before metal existed.
See now
this is what rockism is. If you approach Mahler's sixth symphony looking for rock and roll cues, you might pick up on something different, maybe even interesting, but you miss out on the best parts of it. It's not metal; it's nothing like metal. I defy any metal head to come up with something like the Alma theme and play it with a straight face.
This is one hour of dense, complex music, with a complex but definite structure (not saying that metal is not complex or structured; it is in different ways I guess); a powerful statement in classically-based harmony and melody by one man, grounded in centuries of western music history. It's pure, unadultered late Germanic Romanticism (very late - he was the last true Romantic, before the first world war more or less confirmed what the modernists had worried about for decades), which is totally different to 'neo-Romantic' metal (that's a thing right?): it is entirely a product of its time and place in history. The focus is entirely on the music itself, notwithstanding its nominally programmatic nature, not on Mahler, not on a narrative (at least, no more than any other symphony since Beethoven's third) and not on the orchestra. The orchestra is merely the instrument through which the world contained in the music is communicated.
Essentially, you
need to approach a symphony like this one differently to the way you approach contemporary pop (using that word very loosely ok? And not in a derogatory way ok? I like pop music!) music. Otherwise you diminish its value. Metal is about (from my limited understanding) being loud, epic and virtuosic, whereas Mahler's music, while being 'epic' (in a different way) is more 'richly' (not a value judgement ok, talking about western classical harmony here guys) developed, and embodies different musical notions altogether.
I'm not being prejudiced or saying that Mahler's approach to music is 'better'; the point is that I listen to Mahler for reasons different to those I listen to 'pop' music for, or even the reasons I listen to Brahms or Schumann. If you only want music that 'rocks out', that's cool, and if Orff does that for you then more power to you. But if that's all you're listening for you'll 'miss out' as well (this is possibly the most cringe-worthy university professor–style sentence I have written but I will leave it anyway)
Anyway, apologies for spreading the rockism meme to another thread, but here is a different way of looking at it.