If a young moviegoer who had never heard of Akira Kurosawa wandered in to see the aging master's Akira Kurosawa's Dreams, he might think he was watching a Japanese Twilight Zone in which all the metaphysical punch lines had been mysteriously snipped out. Dreams, a mostly tedious eight-episode movie, finds Kurosawa flailing about in an unusually sour, didactic mood. One of the early scenes is haunting: A boy visits the field where his family had chopped down an entire peach orchard, and the fallen trees ''reappear'' as singing human accusers. When a blizzard of purple peach-tree leaves flows across the screen, the moment has an enchanting purity. In another scene, Martin Scorsese appears in a straw hat as Vincent Van Gogh, which is rather silly (I doubt anyone in the 19th century spoke half as quickly as Martin Scorsese) but at least diverting. But then Kurosawa stops dreaming and starts scolding. The picture devolves into a series of obscure, finger-wagging lectures on the subjects of nuclear war, pollution, etc. Even for those seeking faint echoes of Kurosawa's greatness, Dreams I'm afraid, is a dud.