Meet Superman!
Most superheroes have different facets to their character, they have their dark sides and lighter sides, whereas with Superman, what you see is pretty much what you get. Does that make it harder to perform the role?
I think as exemplified by the film, he does have a character arc -- which, I trust, is present in the film. He may not have vices or be a dark character, but he is not uni-dimensional either; he has to learn things for himself, he has to grow.
His father can teach him the math and science, he can teach him about the universe, but, until he experiences love, he doesn't know how to deal with it. There are certain things you can only learn by hands on experience and that is his growth, that is what we see in the film, that he is learning how to adapt and how to live and deal with love -- for me, that is a big journey, and I think that is exciting for audiences too because that is what we are all here on earth doing, learning to deal with things life throws at us.
And then there is this big guy, this powerful presence, with all the strength you could ask for and all the powers, and he has to cope with the same things the rest of us do, he has to learn to deal with it and grow as he is learning, and that I think makes him all the more real.