Showtime’s new teaser for Dexter’s upcoming sixth season makes the show look dark and scary, but it also highlights the show’s major weakness: Dexter is incredibly repetitive. The trailer rattles off everyone’s favorite vigilante serial killer’s former foils — the Ice Truck Killer, Doakes, Miguel Prado, and the Trinity Killer, though there’s curiously no mention of Jordan Chase — which makes it clearer than ever that they all presented very similar obstacles for Dexter. Someone’s too close to the truth! Dexter finds that person revolting and fascinating! LaGuerta does something ill-conceived that somehow gives Dexter extra wiggle room, and then Deb gets overly involved with someone unsavory. Just when it seems like everything will be exposed, Dexter manages to kill his foe, and thus preserve his secret and add another slide to his specimen box! Dexter is a good show, but it hasn’t exactly reinvented itself season to season.