Here were my thoughts on how I'd like Luthor to be portrayed, from the "Character Portrayal" thread:
LEX LUTHOR
I'm open to him being either a Machiavellian business tycoon, or a mad scientist supervillain, as I don't think either portrayal has really been done full justice on the screen before. Perhaps - tying into my previous post - he starts out as beloved CEO of Lexcorp, but it's the dogged, determined journalism of the Daily Planet and Lois Lane in particular that ultimately brings him down and has him recast as a feared and hated villain in future films.
But whatever incarnation he's in, there are certain qualities I want to see. Lex Luthor thinks he's the hero. None of this Gene Hackman "I'm so evil, the greatest criminal mind in the world, BWAHAHAHA!" stuff. He sees himself as Prometheus, stealing fire from the gods and bringing it down to man. He thinks that if only he can get rid of Superman then he can cure cancer and end world hunger and be the adored leader of a utopia of scientific future-people. But that's not true. He's incredibly intelligent, a genius even, but he's not as smart as he thinks he is. His own deficiencies, his own deeply personal shortcomings and inadequacies, mean that no amount of praise, no amount of validation, no amount of recognition can ever be enough for him. He needs something to blame his inability to be as great as he wants to be on, and so everything is Superman's fault. If it wasn't Superman, it would be someone or something else. There has to be an enemy, other than himself.
In a lot of ways, Lex is a classic racist. He says we can't trust Superman because he's not one of us, he's something inhuman. He's an outsider, and only he is brave and clear-sighted enough to stand against him as a self-appointed champion of humanity. And the tragedy of it is that Superman is a better human than Luthor can ever be.
But it's important we see the parallels between Luthor and Kent. Both had humble beginnings, raised in Smallville. But while Clark had the unconditional love of the Kents, Luthor had the cruelty and the constant criticism of his father. While Clark wears his identity proudly - be it his Smallville upbringing as Clark, or his Kryptonian heritage as Superman - Luthor is ashamed of where he came from, and has spent his adult life trying to erase that part of himself, twisting and coiling himself into this grand vision of transcendant genius that he feels he should be.
Superman can fly through space and into the stars, but comes down to Earth to walk among us. Lex Luthor is an ordinary man, but builds the highest skyscraper in Metropolis and locks himself in it like an ivory tower to keep himself separated from the unwashed masses. He is someone that, like Superman, has great power, but unlike Superman, doesn't want to share it. He wants it all for himself. He wants the adoration and love that Superman gets, but without realising that he needs to give just as much back for it to work.
Look at how Luthor has evolved throughout history, and you can see in his various incarnations what he stands for. In the era of the atom bomb, he was the irresponsible scientist abusing advances in technology. In the era of "greed is good" and yuppie culture, he was the amoral representative of big business. In the era of an unpopular war and an even more unpopular Government, he was President of the United States. And now, he embodies all our own prejudices and shortcomings. Just as Superman represents the best in humanity, Lex Luthor represents the worst - everything in us that is selfish and petty and small.