Heavy Metal needs no introduction. Everybody knows what it is; the most aggressive form of rock music (in competition with its erstwhile greatest enemy, punk), the loudest, the druggiest, the most doom laden, the most cartoonish, the most sinister, the favorite music of tortured teens the world over; the music people are most likely to "outgrow".
Its drawing points are simple and obvious; beyond the sheer central nervous system stimulation of the bone crushing riffs, heavy metal's lyrics are pure escapism -into a world of fantasy or a world of Satanism and death-, its image is staunchly in-your-face-mom variety teen rebellion (and twenty-something angst), it is generally pro-sex (although some bands never even went near sex), pro-dope, anti-religion, death-obsessed, anti-authoritarian, vaguely fascist, aggressively anti-war (in many cases) and all manner of other "taboo" subjects.
At its most heroic, heavy metal is indeed legitimate art and legitimate thrills. Led Zeppelin still tower over all who approach for their intensely musicianly approach to pure wallop; bass-drum heavy skin pounding, spine-tingling powerful guitar riffing that plundered the blues shamelessly, a definitively capable front man, whose voice could win over males and females with its range, soars, galvanizations, pomp, and even sensitivity. Lyrics that bore no relation to the world at large; a Led Zeppelin album was just as much an escape into fantasy land as Pink Floyd or Yes; bands like Metallica, Megadeth, Slayer, and Pantera still serve this same essential function of escape, no matter how the older metal heads might not dig the newer bands. After all, heavy metal never was made for old people; it was for the young.
At its crassest, heavy metal is the sum of all the ridicule and scorn that has been heaped upon it for decades, famously spoofed in the film This Is Spinal Tap. It can be musically ignorant, gratuitously dumb in its lyrics, stupid and irresponsible in its worldview, noisy and irritating, and appallingly hypocritical as it laughs all the way to the bank.
Born in 1969, its history is colorful, with all sorts of characters and tales of on-the-road debauchery and decadence. It is a history rife with drug abuse and early death, gold records and limousines, ridiculous pomposity and moments of menacing inspiration. It is the genre that has retained its popularity the longest; aside from a brief lull in the late 70's-early 80's (and a slight one currently) it has never managed to lose its popularity with the teen market.