I enjoyed it, but wished they had done everything differently.
Start from scratch, like they did with Batman Begins. When both franchises run out of steam as they always do, make a Worlds Finest on straight to DVD.
Can keep Lex as the villain, but make him a billionaire and have him doing shit behind the scenes. We know he's a wrong 'un, but its always implied and not actually shown. Have someone else more spectacular be the bad guy. Lex gets away with it completely. Then in the sequel you could have him running for President or something.
Since he is so powerful, they need to add in problems that he cant solve so easily. Lex is trying(and probably succeeding) to bang Lois. So when Clark has suspicions that Lex is a bad guy but no proof, everyone has a good reason to doubt him. You could even have a completely Clark subplot that involves investigating Lex. Main plot is Superman doing super things. Since Lex is now a sub character, all the time wasted with him in Returns could be used for more Super action.