(My knowledge of theory is admittedly limited, so please feel free to be more elaborate in your replies if you're so inclined) That said, within metal what is your favorite musical idea, trait, or pattern? A certain tuning? Breakdowns? Blastbeats? A particular type of soloing? Etc. I'd have to simply go with prominent sustained notes. It's particularly common in my favorite genres of stoner & atmoblack. Be it a prominent bassline, or a rhythm guitar holding a sustained note or a slower/more drawn out riff while the lead solos or plays a faster riff over top of it. Or even when the drums take on more a narrative over top of the guitar such as parts of Nile's Unas, Slayer of the Gods. It's nothing particularly special or rare, but I'm just a sucker for it.