This gory take on the Jack the Ripper legend, starring Johnny Depp as an opium-addicted detective, wants to be a thinking person’s slasher flick, even quoting the killer as saying, “I gave birth to the 20th century.” That’s an intriguing boast, but sibling directors Albert and Allen Hughes, adapting a graphic novel by Alan Moore, are so concerned with spilling blood and guts they never really explore what the statement might mean.