Last night I watched Superman Returns because I was bored. I've loved this film ever since I saw it the first time, and that was quite a while after it was released to the cinemas. So I missed all the hype. I hate hypes. Everytime I see it I notice different things. And as JustSomeGuy said, from the objective viewpoint there aren't much flaws.
So, yeah, to make a long story short, I do agree with him (JustSomeGuy). You don't have to know a lot about Superman, you just have to know the basics of his relationship with Lois, and a little bit about who and what Superman is. Other than that, the film makes it all pretty clear. I loved the emotional feel of the film, I keep saying Brandon Routh did the best he could with the handles he was given.
And what JustSomeGuy said.