"Did you just bring a bomb into a hospital?"
In the war between Walter and Gus, Jesse served as the pawn between the two sides. Throughout this season, both Walter and Gus have tried desperately to get Jesse on their side as a means of survival. In Walter's case, he found there to be no other way of killing Gus, except through Jesse. As for Gus, he grew tired of all the trouble that Walter brought along with him. However, Gus could not totally bring himself to kill Walter, without Jesse's permission. Or at least that was what Walter wanted Jesse to believe. After all the deceptions, it came down to Jesse providing the information of Gus visiting Hector at the nursing home, that gave Walter the upper hand, allowing him to finally get close enough to Gus.
The visits to the nursing home showed a different side of Gus. His arrogance. In fact, his arrogance was only ever seen in his interactions with the cartel. In a flashback to twenty years ago, it was Gus' overconfidence in his business practices that got his partner killed by the cartel. This explained why Gus had so much severe hatred of the cartel, and why he tried to run his drug business as independently from them as possible. While Gus visited Hector, he made the mistake of bringing Jesse along to brag about how the cartel was killed, for no other reason than to tear Hector apart even more. With arrogance, also comes the underestimation of others, a foolish sense of invincibility, and an inability to accurately predict the future. As Hector had lost everything, he took Walter up on his deal, and did the one thing he was capable of doing. He rang his bell, and went out with a bang.
What makes this scene interesting, is the portion that is not shown. This allows for the viewer to be curious, and speculative in order to fill in the gaps of the story. This makes the show more dramatic, and adds that element of suspense that would otherwise not be present. Knowing this formula, it was pretty obvious that in the previous episode, Walter was not going to remotely blow up Gus with a car bomb. It was just too predictable, as this attempt was shown. However, it is the unknown between what happened between Walter and Hector, that made that explosive scene so gripping and almost unforeseeable.
It was further implicitly revealed at the end of the episode, that it was Walter that was behind Brock's hospitalization. This went to demonstrate just how low Walter can stoop, in his manipulation of Jesse, and the means that he can resort to in order to meet his goals. The final scene also provided an explanation of the incongruency between Gus taking offense when he was asked if he ordered the death of a child, and Walter saying Gus had no objections to killing children. Walter has indeed turned into a whole new person, one that has even less restraint than Gus.
With Gus dead and the cartel eradicated, in typical Breaking Bad formula, past actions will have consequences, and Walter will realize just how wrong he was in saying, "I won." In addition, there leaves one final plot-line that still needs to be played out. Next season of Breaking Bad will also be its last, and the conclusion of the series will inevitably be Hank discovering that Walter is Heisenberg.