[Udik]

There are two comments, yours and another one, that suggest that I might not ever been a "true listener" of heavy metal. That's the "no true scotsman" fallacy. Why can't someone who sincerely enjoyed a genre of music in his teens outgrow it? No, better, outgrow the whole idea of genres.

Heavy metal is (you have to admit that) a pretty rigidly codified type of music. It requires a certain set of instruments, with few variations (I still remember debates in the eighties on whether keyboards were kosher). It mostly deals with a fixed set of themes. It sounds in a very recognizable way, so it's rather easy to classify songs that fall into it. Performers dress in a codified way, also easily recognizable. (To all these points there are obviously a few exceptions here and there, as always.)

As for the richness of subgenres: it seems to me that these subgenres are just the partitioning of a fixed space of immutable size. The urge to classify them is another proof of the fact that the rules of the genre are so rigidly codified that the slightest deviation or emphasis on an element requires (or allows) a new classification bucket.

[CWuestefeld]

Heavy metal is (you have to admit that) a pretty rigidly codified type of music. It requires a certain set of instruments, with few variations

Nothing could be further from the truth. For example, the OP itself talked about "folk metal", a sub-genre that uses traditional themes, musical styles, and instruments.

It sounds in a very recognizable way, so it's rather easy to classify songs that fall into it.

Again, you've missed out (and even claimed that it never happened) a HUGE amount of evolution. Metal fans love to bicker and debate, and you'll see, for example, discussions over whether the evolved Opeth, that eschews their older death metal trappings, still counts as metal at all. In the proggy sub-genres that I enjoy, there's ample debate over whether a particular band or song is prog metal or "just" prog rock.

In its infancy, much of metal was dismissed as being stupid, three-chord performances. It's evolved so that today, it's undoubtedly the most technically demanding genre within the entire poo & rock oeuvre. Bands like Meshuggah, or the whole math-metal sub-genre, are performing music so technically demanding that no high school garage band is going to get near it.

In its expansion into these prog, technical, death, extreme, folk, etc directions, there is no doubt that the variety of expression covered by metal today is many orders of magnitude greater than in its younger days.

[Udik]

For example, the OP itself talked about "folk metal", a sub-genre that uses traditional themes, musical styles, and instruments

Folk metal is actually well inside the tradition of heavy metal, that spans from the black/ gothic to the epic and fantasy themes. By the way there's even a more extreme musical genre called "folk": where people from different regions of the world perform actual folk songs strongly connected with their real traditions. Can you imagine, you can actually listen to folk music outside of the rules of heavy metal? That's extreme.

Metal fans love to bicker and debate ... over whether ... still counts as metal at all.

Exactly. A little bit of evolution or variation and people start debating whether you're still in the group or out. That's silly.

And oh yes, I've listened to my share of Yngwie Malmsteen and Cacophony. Heavy metal fans are certainly very proud of the raw technical skill (which is, in fact, just speed) of their players. But it's a sort of pissing contest, who can play the riff or the solo faster is not a good meter of one's musical talent or skill.

[CWuestefeld]

which is, in fact, just speed

Sure, if you're talking about just Malmsteen or Cacophony. But again, you really have missed the evolution. Things have moved well beyond that in the 21st century. For just one example, the band Meshuggah that I mentioned requires the performer to shift fluidly between bizarre odd time signatures. It's debatable how much this improves the musicality, but it's an advanced skill that requires a ton of experience; some small amount of this was visible in the era you're referring to, but the evolution has been, well, extreme.

[Udik]

Listen, I can understand that for a serious chess player, the style of chess has evolved enormously during the 20th century. That doesn't make it less of a strictly codified game. Anyway, it's a matter of tastes..

One last observation. I remember that in the early nineties, a single chord from Nirvana - I was hearing them for the first time- was enough to make me say "this is not heavy metal" (I was actually pretty disgusted by that sound at the time :)). How is it that after more than twenty years (during which I haven't listened to new metal bands), 3 seconds of Meshuggah are enough for my brain to categorize them with absolute certainty as heavy metal?

[ionised]

> Heavy metal is (you have to admit that) a pretty rigidly codified type of music.

No we don't have to admit that.