*** 1/2 VARIOUS ARTISTS “The Rocky Horror Picture Show--15th Anniversary Collection” <i> Ode/Rhino</i>

Richard O’Brien’s kitschy, sci-fi/glam-rock “Rocky Horror Show” stands as not only the best rock musical ever written, but probably the last very good one. Besides his rare gift for writing actual rock songs for the stage, O’Brien’s genius was in depicting the sexual revolution literally as an alien invasion, and it was a funny, brilliant metaphor for moral upheaval.

Such symbolism is pretty much lost on most of the toast-tossing, corset-clad cultists who see the film as an excuse for romper-room midnight-movie decadence. Their folly doesn’t diminish O’Brien’s original achievement, the nearly 20 songs of which are well-documented (spread over four CDs, a little too well-documented) in this overly exhaustive box set.

The 1975 film score is the one essential disc therein, an improvement over the earlier Roxy cast recording also included. The other two CDs consist of rarities, foreign-language versions, additional recordings by cast members and tracks from the mediocre sequel, “Shock Treatment.” It’s nice to finally have several excellent numbers that were cut from the movie’s soundtrack, but the long-awaited “Sword of Damocles,” for one, sounds as if it was mastered from a second-generation videotape. Did some of the master tapes get caught in a time warp?