Its fictitious director, Marty DiBergi, only too happy to subscribe to the journalese du jour, labels this movie a "rockumentary." We might suggest in that same spirit, and in that same Time Inc. style, that its actual director, Rob Reiner, describe it as a "mockumentary": a put-on (or -down) of all the rock concert/tour documentaries, with particular indebtedness to Martin Scorsese's The Last Waltz. (Certainly the beard and the furrowed brow and the subsidiary role as on-screen interviewer, in addition to the baptismal name, bring to mind Scorsese.) Every episode that might be said to go too far in search of a laugh can be matched with one that goes exactly far enough, and with plenty of others still left over. And, in any event, the performances of Michael McKean and Christopher Guest as the co-founders of the band -- David St. Hubbins and Nigel Tufnel respectively -- function almost gyroscopically to compensate for any deviation. They, and to a lesser extent Harry Shearer as the lower-profile Derek Smalls, never drop their masks long enough even to wink at the viewer. If, despite all that, there is any damaging complaint to be raised, it would just be that the filmmakers have made things too easy on themselves (and on the heavy-metal fans in the audience) by focussing on a group so precipitously and pitifully in decline. Heavy-metal fans will be able to reassure themselves that the egregious badness of the music, and the broadness of much of the humor, are necessary to the parody. Heavy-metal non-fans on the other hand, or fans of parody in general, will feel quite justifiably that no such precautions were needed. It is easy enough for the latter, of course, to laugh whenever they want to at the bona fide "heavies" on MTV. But that's a colder and lonelier experience than this is. (1984) — Duncan Shepherd