First off, back story does not always work. Just watch Malificent and Star Wars Episodes One and Two.
Injustice took chance by making its story arcs last a year. This solves a few problems like having too much material but not enough time to work it out. The downside is it has to have the material to fill in a five year gap without conflicting with what the video game set. After all, since these comics are based on the game, it must adhere to the game’s storyline above any creative thoughts they have.
Every year seems to have a theme. The first year dealt with the issue of Superman taking his first blood in Joker and establishing himself as ruler of Earth.
The idea of someone as good and righteous as Superman turning evil creates a real predicament for people who are good because they remember the good man he was and ignore the evil they are becoming. Further, this arc really showed how some people draw their lines in the sand.
This arc showed the problem of choosing sides and the price people pay for doing what they think is right. Whether that means they compromise their morality or they lose someone they loved, no one in this story walked away consequence free of their decisions.
The story takes a proper progression of events using characters who would intervene when they think they see and opportunity. Villains like Lex and Sinestro make marks while heroes like John Stewart and Black Canary show the fans exactly what it means to be a hero.
With Year Three starting up with a focus on Magic rather than lanterns, this journey seems to be one worth watching.