Well, yeah, it's no secret that Superman's level of power makes it hard to have any real drama in his book. Although "All-Star Superman" actually makes him even more ridiculously powerful than the mainstream version, but STILL managed to have more dramatic tension.
And yet he can't ever really defeat Lex Luthor. Luthor goes to jail, fakes his own death, gets banished to another dimension etc pretty frequently, but it never lasts. He's got to be there because he's part of the ingrained identity of the series. Even worse, as times goes by he has to get progressively more and MORE evil in order to avoid becoming redundant.
Take "52" for example, an AWESOME series that I really loved. Luthor looks like a particularly big scumbag in it. But when he gets his comeupance, I really didn't care, despite having waited nearly fifty issues to see it happen, because it's not like there's any real consequences for him.