Apologies, I probably haven't expressed my point clearly - Lex Luthor, although I think he's a good villain (I like Lex more than I like the Joker), is in my opinion simply not that interesting cinematically. He doesn't translate well into a movie villain. In movies you don't have the time to establish a character like you do in a comic book run or a tv series, so effective villains need to be captivating or at the very least have a good visual gimmick.
Lex Luthor hasn't been a successful movie villain. I like Gene Hackman but his Lex was little more than comic relief, and definitely nowhere close to being a timeless movie villain. Kevin Spacey's Lex was boring and had no defining psychology.
Think about all the truly great movie villains. Darth Vader, The Joker, Hannibal Lecter, Anton Ciguhr, Bill the Butcher, Magneto, there are all larger than life characters, and they are either exceptionally archetypal (Ciguhr, Joker, Darth Vader, Lecter) or extremely complex and borderline sympathetic (Bill the Butcher, Magneto), sometimes both.
Lex Luthor has never really been all that complex, and every time the comic have managed to make him seem a little deeper or more sympathetic, you must realise that because this was in a comic book, that a lot of that was building on years and years of dedication and goodwill on the part of the reader. Making Lex more interesting in a comic is easier because the reader has a whole bunch of background and stories to base his understanding of the character on, so not only will there be less groundwork to do, but the reader will usually be quite open to seeing a character's psychology fleshed out more.
Here we have a 2 hour movie. And we need to say everything there is to say about this version of Lex Luthor in those 2 hours. Frankly, I just don't think the character has enough impact, visually or psychologically, to make a brilliant movie villain. He doesn't look cool or freakish or anything other than bald really. He isn't psychotic like the Joker or Hannibal Lecter. He doesn't have superpowers like Magneto, he lacks the moral complexity of Bill the Butcher, he's not a tragic figure like Khan or Darth Vader. He's just not a movie villain in my opinion.
Terence Stamp is amazing, and his Zod was cool, but I still would argue that (my own fanboyism aside) Zod was not a great movie villain. The fact that he's got a good stare and sounds awesome saying kneel before Zod doesn't make him a great villain in my opinion. He was cool, but also a creature of his time.