Anyone can show an exploding car, or a firing gun. Delaying the explosion and the bullet is an art. Twisting the guts of the viewer without letting up, and making that insane level of tension make perfect sense, is mastery of the art. We buy it. All those slow episodes we sat through early in the season, picking up details and feeling out the characters ... that provided the structure that episodes like this one rest on.
There are two other themes intertwined with the suspense: mystery and allegiance.
First, mystery. How the hell did Brock get poisoned? Last time we saw The Cigarette, it was sitting on Jesse's living room floor. It's unlikely that it was forgotten there, and unlikely that Tyrus would know enough to use the poison. But it fit perfectly with the theory that Gus would have Brock poisoned to inspire murderous rage in Jesse. There's nothing so tense that a little paranoia can't be added. And there's another mystery: how can Jesse justify knowing that the boy took a very rare and lethal poison? Andrea is a mother before she's a girlfriend, and there's no way she'll let this matter drop, no matter how good Jesse's intentions.
And this dovetails into the allegiance theme. With this poisoning, Jesse is ready to kill Walter, just as Gus would have him do (after nakedly trying to sway Jesse's opinion earlier in the episode). But just as Jesse's about to pull the trigger, a newly-familiar laugh bubbles out of his target: the ruthless Heisenberg pieces together what Walter alone cannot calculate. And this unlikely scenario of Gus poisoning Brock plays so perfectly off of Jesse's soft spot for kids and Jesse's learning that Gus threated to kill Walter's infant daughter (he heard it from Saul first, which is probably why he believed it) that Jesse's core allegiance has shifted.
So Saul skips town. Aw! We'll miss Bob Odenkirk (for a time), but it was time for his character to make a break for it. Many touches, big and little, made sense from the characters' perspectives. On the "little" side, there's Skyler asking the agents for a cigarette, and Walt Jr. grousing about his pigheaded dad staying in harm's way. On the "big" side, there's Gomez taking Hank's challenge to do a knock 'n' talk, coming within a hair's breadth of revealing everything.
And on the "huge" side, there's Gus and his preternatural sense of danger. He avoided a messy death by nothing more than his instinct. A twist like that would be impossible -- un-buyable -- without the work this show has been doing with Gus since late-second-season. Now, he is going to find out that there was a car bomb, and he will suspect both Walter and Jesse. At one time, Gus could have found an accord with Walter's cool reason and with Jesse's fierce morality, but no more. No more accommodation. Conflict is not just unavoidable, not just imminent. It's in action. The final two monsters left, Gus and Heisenberg, must do battle.
There is simply no more they could have done with this hour. I rarely rate anything a perfect 10, and Breaking Bad has had several perfect hours. This episode joins "Bag's in the River," "737", "Over" and "Half-Measures". In my opnion, no serialized drama on TV has knocked 'em out of the park like this.