Prone to shallow ponderousness, Prometheus assumes the air of a blockbuster-with-brains that links the genesis and the ultimate fate of mankind with a galactic quest for the mysterious beings archaeologist Elizabeth Shaw (Noomi Rapace) calls the "Engineers" because "they engineered us." But it works best when it steps back from contemplating the cosmos to enter the domain of flesh-and-blood and hereditary terror. There are a few set pieces here that will find a place of honor among aficionados of body horror and all things clammy and viscous, gyno-phallic cave creatures and a scene of self-administered surgery that will stain the memory long after such significant-sounding bits of dialogue like "That being said, doesn't everyone want their parents dead?" have gone. The script, by Jon Spaihts and Lost's Damon Lindelof, originated as a prequel to Alien, director Ridley Scott's first hit, before developing into its present spin-off form. Rather than setting out, as scriptwriter Dan O'Bannon did with the original, to build the ultimate creature feature, these gimcrack philosophers have loosely sown Prometheus with Big Themes in hopes that one might perchance take root. Scott is swinging for the fences here — he is 74 and perhaps looking for a career-capping legacy film to tackle life, the universe, and everything — but his gifts have coarsened considerably over the past decade.