You should read this, as you look at the greatest metal albums, what you’ll notice is that often, they are composed of eight to twelve songs that all sound relatively the same, but on repeated listens, each one becomes unique and stands out (the best examples of this are Immortal, Demilich, Massacra, the first Morbid Angel album, Graveland, and early Emperor). As a collection of baroque pieces or Gregorian chants, it all sounds like on the outside, but each individual piece varies greatly, at least to a trained ear.
This is because good metal, more so than other forms of popular music, is structural music with narrative song forms, meaning that the music is composed of a series of repeated phrases (riffs) that follow each other and interact with each other in ways you’ll never hear in a Britney Spears or Jay-Z song. It’s more complex not only musically, but artistically as well, due to the fact that some form of ideation or ideology often precedes the composition of the actual songs.
Metal isn’t really focused on sounding appealing to commercial tastes, and unlike certain odious trends, it is not about being “different” or “diverse” by throwing in a bunch of random elements, styles, or parts, and feeling smug and “open-minded” for doing so (examples of this? Between the Buried and Me, Opeth, Psyopus, Dream Theatre, Dillinger Escape Plan). Like classical music, it is more focused on actual composition, which is more mathematical/logical and simultaneously more emotional/artistic than most other forms of modern music, which are socially or financially motivated.
You could diagram it like this:
“Heavy” ideas, realistic values, or interesting observations — gt; Musical representation of that idea (or as close as you can get) — gt; Several ideas grouped in logical / emotionally powerful order — gt; Good metal, folk, classical, neoclassical music.
“What most people want to hear” — gt; Familiar musical ideas — gt; Verse-chorus-bridge format — gt; Pop music, hip hop, soul, emo, etc.
So if you want to write good metal songs, there are several basic traps to avoid. For one, music that has nothing to say won’t stand the test of time, no matter how virtuosic or well-put-together it maybe (I’m looking at you, Necrophagist!). Second, if you’re going to form a band, know that metal left behind the verse-chorus format over twenty years ago. And lastly, throwing everything and the kitchen sink into your songs doesn’t make your music smart or artistic, it usually just makes it distracting and ugly.
When you find what you want to say and the media / aesthetic in which you choose to say it, focus on writing the best material you can, composition-wise, and make the music you want to hear – it doesn’t matter if it”s cut from the same cloth as Bathory, or has the exact same product as Incantation. There is nothing wrong with an honest tribute (as long as it offers a new angle and isn’t just a blatant ripoff), and it is perfectly reasonable to stay within the orthodoxy of metal imagery, lyrical topics, and aesthetic values. Because if there’s poetry within them, your songs will be collectively an eternal meditation on the logical architecture of reality and the irrational language of emotion all at once.