Watching that behind the scenes feature...the casting was wrong to begin with, but they miss the essence of the character, this version of Lex Luthor thinks he's saving humanity from Superman and that sucks.
For me, it's always been that Lex's point of view is, you (Superman) want to save humanity and I want to save humanity...(or...just 'this is my city, and I deserve the credit, not you') one of us has to go.
Moreover, it's about Lex Luthor hating Superman because he desires his power. They've made this too complicated.
Maybe they made him too smart. I just wish they didn't take it too far where he actually had Martha kidnapped.
I don't know what it's going to look like for them when they're on the screen together again.
The chemistry, if you will, between Superman and Lex will feel so different when they are confronting each other. Superman will probably hate Luthor more than he has in any previous incarnation, as this Lex actually kidnapped his mother and threatened to kill her. I mean Superman will look at this guy as more of a crazy clown (honestly, he seems crazier than the Joker) psychopath lunatic.
It's hard to describe what Lex is, it can be argued that he is crazy, but Eisenberg's portrayal is more like batsh** crazy unlike the actual character. Dangerous? Eisenberg's Lex had that, yet still somehow seemed wrong. Eisenberg's age, his physique was all wrong.
His personality was the biggest problem though. Jokerish. He's like a villain from the TV series, Gotham, who under the right influence, could take a turning point, and maybe form into a crazier villain.
Even if he does start acting like the Lex we know from comics, into a more, serious and sane version, Eisenberg will still be considered miscast due to his kid-voice and height.