The only negative to this movie...

Rating: Null/10 (13 November 2000)

...is that people mistake it for being an accurate reflection of an entire genre. In its purest form, British doom metal was actually concieved as a form of rebellion against an agonisingly empty and desperate existence in a city that still had bomb damage left over from World War II. Similarly, Norwegian black metal was concieved as a form of rebellion against a Christian government that had stripped the country of its rightful heritage. So no, neither art form (and those are they only basic true forms of the music that plastic bands of the 1980s like Poison et al were trying to imitate) is as childish or asinine as this mockumentary wishes they were. They both are marked by strong social, political, and psychological messages that ring very true even thirty years after the first album of the elder genre came out.
As a sendup of the lame, plastic, tryhard imitations that the major record labels of the 1980s flooded the market with in a cheap attempt to weaken the legacy set by Black Sabbath in the 1970s (and still admirably held up by such bands as Cathedral and My DyING BRIDE), however, Spinal Tap is impeccable. In fact, one can argue that the message of This Is Spinal Tap is to remain true to yourself. Spinal Tap are obviously a clone of all those bands out there that were created in order to fill a booming market, and the film shows what happened to the 'Tap when the fickle tastes of the market changed, leaving them out in the cold. In that sense, it was well ahead of its time, as the market for soft, poppy versions of what Napalm Death and Cathedral did so well during the mid 1980s and early 1990s (respectively) didn't actually dry up for another six or seven years after the film's release. Excellent foresight.
Another myth that this film puts forward is that a band will sound the same regardless of who is drumming. Anyone who's heard the difference between the My DyING BRIDE albums of 1991-1996 and then heard the two that were released in 1998 and 1999 will tell you this is far from the case. While it is hard to distinguish oneself on the drums, those who achieve it are all the more notable for doing so. But one thing I like about this film is how it illustrates one truth: the more effort a band puts into posing, the more plain and ordinary their music generally sounds.
So if you're searching for an accurate reflection of a musical genre, then skip this film and grab the remastered version of Black Sabbath's "Paranoid" album instead. But if you want to laugh yourself senseless at some jokes about poser stupidity and some hilarious references (one guitarist's voice is identical to a manager's from Led Zeppelin's "Song Remains The Same" movie), then this is the film for you.