Noblesse Oblige.

Similar to Grimmjow's defeat and Nnoitra's death, we see some of Barragan's history before his final breath. This was very interesting, because it revealed how Aizen took over Hueco Mundo: by dethroning its current king and making him his underling. Of course, someone with as much pride as the king of Hueco Mundo cannot swallow this, and Barragan's final act thus was an appropriate attempt to take Aizen's life.

Seeing Aizen and Gin back in captain clothing was nostalgic and pleasing. Also, we saw more of Kyoka Suigetsu in action. This part sort of confused me though. I was under the impression that Kyoka Suigetsu's Shikai creates a powerful illusion on all who witness its release. However, when Aizen muttered "Break, Kyoka Suigetsu," he managed to wipe out all of Barragan's army. Was this just an illusion to get Barragan to obey him or does Kyoka Suigetsu have a side ability of raping everything in sight on Aizen's whim?

Several things I want to note:
The captains and Visoreds were unphased at Barragan's betrayal against Aizen.
Aizen's coolness caused the axe to disentigrate. =P
Barragan's power is inconsistent: rots away buildings but fail to rot his crown; rot leaves the bone like in Soifon's arm's case, yet it rotted away all of Barragan's own body, which is a skeleton.
Someone thought Barragan's release form seems weaker than his normal form and I agree. Barragan managed to break a captain's arm in an instance in normal form, yet couldn't hurt a vice-captain with his most powerful ability in released form.