The best episode of the entire series (in my opinion, at least) starts with Luthor and the other members of the Legion of Doom that survived, coming to the Justice League for help.
Superman agrees to let the Legion join the fight, seeing that they are going to need all the help they can get to defat Darkseid.
All over the Earth, dozens of Parademons attack, but find members of the Justice League ready for them. The ultimate fight occurs in Metropolis, on top of the Daily Planet building, where Superman, Batman and Luthor await for Darkseid to appear.
Superman fights Darkseid again, this time determined to destroy him once and for ever. Superman finally admits he has never before shown anyone his true strength, and after a superb speech, punches Darkseid all over the city. However, Darkseid tricks Superman and entraps him inside the Agony Matrix.
Meanwhile, Luthor confronts Metron and tells him to show him how to defeat Darkseid.
When all seems lost and Darkseid approaches a fallen Superman, while holding a Kryptonite dagger, Luthor returns and gives Darkseid the only thing he ever wanted: the Anti-Life Equation. Darkseid touches it and both he and Luthor dissappear in a flash of light.
The fight is over, and the members of the Justice League have won; Earth is saved. The seventh founding member has returned, after missing from the last few episodes, and together with all the other heroes, run down the stairs of the Metro Tower towards a new adventure, an adventure we unfortunatelly might never see.