This Is Spinal Tap more or less invented the mockumentary genre with this parody of a documentary about a fictious hard rock band named Spinal Tap. Much of the script was improvised, a fact which is occasionally transparent but mostly successful. At times, the film is hilarious -- watch for scenes concerning a new album cover, an amp that is "one louder," and a slip-up involving Stonehenge -- while at others, it drags. Tighter editing might have been a good idea, but so few films ever get as good as this one does at its best, so why complain too loudly?