Breaking Bad Season 4 takes the show to its darkest season overall as it depicts Jesse and Walt entertaining truly into the underworld of drugs where death is a daily event. The season seems defined by pain, paranoia and a certain despair as the pair deal with the fact that they've only survived certain death through the blood sacrifice of another. There are no reprieves for anyone in this season as Walt is constantly reminded by his potential death at the hands of his former ally, and still employer Gus Fring, while Jesse is haunted by the murder he had to commit to save his own life. This season is also notable in that it allows Walt's wife Skyler to come into her own as she begins to be changed by Walt's own corruption. There can be few comparison made to the tension of this season which perpetuates through every story, as everyone is on the line. I think the most fascinating element is that they manage to make you even invested in Fring as almost a side protagonist as you sympathize with him in his own revenge story. Then it somehow still easily transitions to being a true main villain for Walt to attempt to overcome. It's downright brilliant season as it is any but a simple cat and mouse game. It somehow takes the stakes further than they had ever been before, and always with the series it advances everything, the characters and the story, so effectively and so naturally.