Thought Affleck was great in ZSJL. I do not really see the difficulty in him going from the dark, angry and lost Batman in BVS to this more hopeful and more traditional type of Batman. That was the point. I personally don't think they were at all trying to act like Bats and Supes were best pals, I mean by the end they got closer cos Bruce had saved the Kent farm, helped resurrect Supes, formed the league etc, but throughout the movie Batman is feeling a lot of guilt for his actions in BVS and feels responsible not only in some way for the death of Superman but also I suppose for the vulnerability of earth to attack now that he is gone. His actions and attitude are driven from being humbled and the realisation that he was wrong about the guy and the consequences of it. Ultimately, Superman saved Bruce from his darkest impulses. He begins to look up to Superman and what he stands for, because he has seen how close he came himself (during BVS) to turning into the thing he has always fought against, because of fear, hate, mistrust. Without wishing to cause anyone or their opinions offence, I think its so easy to rip on the Martha line, but there is more going on here than that.