(If this topic should be in the Metal board, then tell me so. I chose this board rather because this subject is less about a metal band/s or music and more about our connection with the ideas that are presented in metal lyrics.)
I've not been listening to metal long enough to absorb a solid understanding of lyrical styles in metal, so I am asking for help. Excuse my lack of experience.
Lyrical themes in metal appear to me to follow trends (naughty word!) throughout the history of metal eras. Much like techniques used in writing and playing metal - the d-beat (Slayer, Possessed) preceded the blast beat (Deicide), which preceded more experimental tempo-shifting beats (Incantation, Suffocation) - lyrical focus shifts between subjects that seem relevant to the time at which they are written (naturally).
In the 1980s metal, I hear a lot about war, especially nuclear events. According to my dad who was a teenager in the 80s, there was much tension even so many decades at the conclusion of the last all-out war between nations. You can even find mentions of nuclear-weapon-based tension in pop music from the 1980s (Escape Club - Wild Wild West). There are also a hanfdul of movies based on nuclear attack (or just invasion - "Red Dawn") made in the 1980s. So it makes sense that this kind of tension among society would bleed over into contemporary metal, which is an art form that exposes tension that would otherwise remain an obscure, paranoiac undercurrent.
The theme of death is a big one from metal's get-go and has remained since. Obviously the fear of death has not loosened its grip on the throat of society since the 1980s (unlike nuclear attack), so it remains just as common (maybe just as relevant) today as it ever has been in metal's history.
Satan and hatred are two subjects that occasionally overlap (Deicide is my best example), but there are the uber-aggressive grindcore acts that focused on hatred as an inescapable consequence of the liberalized society mired in superstition and anti-aesthetic utilitarianism, and they rarely cross into religious commentary (except to decry the oppressive methods of modern Christianity's offshoots). Then there are those that took a step back and delved into the conceptual aspect of Satan as a liberator; Satan introduces chaos into the rigidity of the hideously mechanical framework of society and therefore offers us new tangents to explore psychologically and socially. Thus it makes sense to glorify Satan even if Satan is not considered a being or entity of any type.
Another constant in lyrical subjects is the relatively simple concept of discomfort. This is a deceptively subtle matter; "goregrind", "brutal DM" and related tripe has driven the subject of brutality and murder into the ground so far that it has popped out the other side of the planet (though I'm not so cool as to be above listening to Disgorged). But there are subjects that do not relate to war or religion that are still extremely uncomfortable for most people and like I said earlier; it is death metal's duty as an art form to expose these subjects. Some examples I have are Death - Spiritual Healing (almost every song), Slayer (mostly everything up to and including Reign In Blood), Blood (most every song I know the lyrics to), and Cryptopsy - Blasphemy Made Flesh and None So Vile.
What are some subjects that are exclusively (or just mostly) relevant in the 1990s or 2000s? Have there been any paradigm shifts in lyrical techniques like the shifts we see in instrumental techniques? Punk rock has run out of stuff to bitch about because the punks won; they repainted their hippy-infested world with a fresh coat of bullshit but were still pushing that agenda of acceptance, tolerance, and equality all along. Will death metal ever get there? Is it languishing or stagnating (lyrically) for an obvious reason or do the subjects of death, war, violence, and Satan remeain just as relevant today as they were three decades ago?