My problem with Mark Strong is that the villains he plays are "evil" and I don't mean that in a religious sense. I mean it as in, they are bad "just because". I don't feel like any of the characters he's played are relatable or understandable in the least. There's not much motive behind the actions of his villainous roles and there's no sense that his characters are simply misunderstood.
And that's something that this version of Lex Luthor NEEDS to have in order to distinguish himself from the previous film incarnations. It seems like they're going through great lengths to make sure that Clark, Lois, and maybe even Zod have motives that people can understand. But I've never gotten that from Hackman or Spacey...and I don't think we can get that from someone who is regularly cast in villainous roles, whether it's Mark Strong, Billy Zane, etc.
In my view, this Lex Luthor needs to be played by someone who isn't well versed in playing villainous roles. They should be aiming to cast an actor who can duplicate the kind of dedication to the character of Lex Luthor that Heath Ledger did for the Joker.