Todd Vanderwerff, at Vox, explains that Breaking Bad succeeded by applying the Shakespearian five-act structure.
[T]he five-act structure gives both the buildup to and fall from the climax whole acts to breathe. Instead of getting stuck in a never-ending second act, much of the story is pushed to the fourth act, or the fallout from the big moment. And on TV, time is everything:
The five acts consist of the following, which I have paired with how each act perfectly corresponds to each of Breaking Badâ€™s five seasons:
Act 1: Something happens to spark the story into motion, and the characters begin making choices that will set everything else spinning along. (In Breaking Bad season one, Walter begins cooking meth and realizes he kind of likes it.)
Act 2: The characters still have a chance to escape their fates, but something in their psyches keeps driving them forward. (In Breaking Bad season two, Walter delves deeper and deeper into the Albuquerque underworld, meeting figures like Saul Goodman and Gus Fring for the first time. The season ends with a â€œwarning from God,â€ in the form of a plane crash.)
Act 3: Featuring the â€œclimax,â€ this is where everything shifts. Something happens to flip everything on its ear, and the story reaches a point where the characters cannot escape whatâ€™s coming. (In Breaking Bad season three, Walter leaves the drug business behind for a while, but ultimately decides to join Gusâ€™s empire. I would pinpoint the showâ€™s â€œclimaxâ€ as the controversial episode â€œFly,â€ in which Walter has the chance to come clean to his closest colleague and decides not to.)
Act 4: The characters, trapped by fate but not yet cognizant of it, are sucked toward the endgame. In a tragedy, this is often when the body count begins to mount (or the audience can see this coming). (In Breaking Bad season four, the war between Gus and Walter dominates everything that happens.)
Act 5: Everything ends, often in blood and horror. There is some quiet musing on what it all means. A few characters escape with their lives, but even they will likely have long years of therapy ahead of them. (In Breaking Bad season five, Walter takes over the Albuquerque drug world but finds himself pairing up with even more unsavory characters. Eventually, just about everybody dies or has their life utterly ruined.)