Wouldn't a superhero sequel be the perfect setting to try out reverse levelling?
You start out a master of all your powers but each battle takes its toll, you slowly start to lose strength and stamina over time as your exhaustion from battle wrecks your physique. With that you lose grip on your more powerful attacks as you're simply not in shape to perform them.
This then ever increases the challenge throughout the game, instead of becoming a near unstoppable behemoth by the mid-point, battling tanks away as if they were flies, you have to become more tactical in your engagements - should I risk fighting that horde or work my way around, conserving strength for those unavoidable confrontations..
I suppose adding a dimension of realism to a man who can shoot lighting from his bare hands (not bear hands as I initially wrote, he would be too awesome for one game) might not gel that well though :)