He's an alien who's invulnerable to most things on Earth, leaves swaths of destruction when he fights, and acts as though he were somehow above the law just because of his powers.

Captain America is a much more compelling character, especially the movie version. Not even originally a particularly noteworthy individual, his strength of character was the deciding factor of why he was chosen to get his abilities. He earned them for being a good person. He's still fundamentally human, and though powerful he doesn't see himself as being above anyone.

If Superman is a symbol of anything, he's a symbol of how far we've come in learning to make interesting characters. He's flat as a board.

Also, Man of Steel was a piss-poor movie.