This is my favorite type of Justice League episodes. Take a bunch of villains (7) and mix them up with a sinister plan to capture the league. These episodes are cool because they show the members of the league working together (more or less) and using their powers to the fullest.
This episode shows how the Secret Society divided and captured the members of the league. They plan to kill them on a stadium but the Martian deceives them and they manage to escape and defeat the Society (what a surprise).
Anyway, the best part of the episode is the final battle, in which the members of the league cooperate and manage to win. This episode is a classic and I liked it very much.