The greatest comic book battles aren't between heroes and villains. You can catch Batman punching out the Joker's magically regenerating teeth any day, but the Caped Crusader versus Green Lantern, or Superman, or Raven "We Need More Women in the Game" Roth? That's something special, even if the excuses for those battles are completely ridiculous. That's Injustice: Gods Among Us — stupidly exceptional.
The reason heroes are doling out equal-opportunity ass-kickings in Injustice isn't as silly as, say, Batman not recognizing Superman with a new haircut or Hostess Fruit Pies. There is a dark impetus to the tarnishing of Superman's halo, but it's a darkness so deep and horrific that it slides right past chilling into clown shoes territory. See, the Joker tricks Superman into killing Lois Lane. He does this by making Superman see her as his once-killer, Doomsday. Supes beats the hell out of her and then flies her into space, where she dies, because one Doomsday-level punch from him wouldn't have mashed her into paste or anything.