This could apply to music, or a lot of things in general, but metal has to make me feel something. Whether it's aggression, energy, introspection, whatever...it has to illicit some sort of feeling. It's one of the reasons why I like so many subgenres of metal, each one has it's feel and fit a particular mood. As I type this, I'm taking a break from organizing my work supplies with some Enslaved blasting. A couple of passages made me stop to listen, so it's not just background noise. I can leave the TV on for that.
It could be the reason why a lot of overly technical-sounding stuff doesn't appeal to me. I like to understand the melody behind a song, even if it's an evil sounding thing. As a musician, I can appreciate the talent and dexterity involved (and harbour slight jealousy that I still can't play to that level myself) but I find a lot of it boring. (Like how I feel about jazz, pardon as I duck and run away...I'll take the comparative simplicity of the Blues any day...) Same with blastbeats. I use them in my own music, but when they're overused I find the impact is lost. Wintersun comes to mind as an example of using blastbeats brilliantly, as does Carcass on the last few records.
Plus, still being able to listen to albums like Reign in Blood, Terrible Certainty, or Seven Churches after nearly 30 years and still getting that "feeling" from them is amazing IMO.
Okay, sorry for the long post. Back to work, and some Carpathian Forest. Thank you auto-shuffle!