If Gibson were playing the mildly crazed Sgt. Martin Riggs of “Lethal Weapon” fame, the streets of Boston would have been littered with bodies after the first 15 minutes of "Edge of Darkness." However, Gibson is more than 20 years older now, and his character in “Edge,” though certainly tightly wound, prefers to investigate before popping off the perps. That’s just one of the problems with “Edge” if you’re an action film fan. If you like your movies more cerebral, “Edge” just might satisfy. The problem from this standpoint, however, is the film suffers from a serious case of obviousitis. You know who the bad guys are from the get-go, so surprises are few, while thrills, for the most part, are lacking.