If you find Superman a bland, boring character then that's fine.
But for me he is more than just a guy who can punch things and fly. He is an alien raised as a man. He is the last of his kind. He lives in a world where he needs to hold back or else he will just destroy everything.
He needs to be the good guy. If not, the world will perish. His moral compass is what really makes hum super - not his powers (well ok, the powers do as well).
He has to live a completely different life in order to protect the people he cares about. I know this is a basic trait for most superheros, but that doesn't make it any less interesting.
But most of all, he has all the power in the world...but he can't save everyone. He can hear someone dying miles away, but if he can't get to them then he has to deal with that. Imagine being the guy who has to pick and choose who to save that day...or even worse, who not to save. That is what makes him interesting.
And plus his powers are really cool.