At a glance, it would appear AMC is taking a big risk with its only huge commercial success. Mad Men and Breaking Bad are Emmy magnets that average 2.3 million and 4.3 million viewers, respectively. But Walking Dead, based on a series of graphic novels, attracted an astonishing 5.3 million viewers when it premiered on Halloween. The season finale in December drew more than 6 million viewers. In the 18-to-49 demo, it chalked up the biggest number ever for any drama on basic cable.