It's superman, I feel like you gotta embrace the zanny, whacky comic book style.
Don't go for a grounded story. The dude is basically a god from another world, the "Man of Steel" grounded guy just made for an obscenely boring and bland character.
If someone had told me the basic script and all the characters in Suicide Squad I would have expected it to be terrible, but it was awesome. I think this Gunn guy knows what he's doing.