Yeah, Metropolis got nuked when her heart stopped beating. Joker basically tricked him by lacing him with kryptonite infused fear toxin. He supposedly finds doomsday and flies him into space only for the toxin to wear off and realise it wasn't doomsday but Lois all along. He watches helplessly (too late to save her) as she dies. Joker rigged a nuke so it would detonate the moment she died. It was awful. Regular Superman gets into it with Injustice Superman basically telling him reigning terror over mankind because he lost Lois was wrong, going overboardetc. Injustice Superman is a villain Superman. He experienced a tragedy but it's no justification for every horrible thing he did afterwards.