i'd make a superman game where you really are invincible, but can still fail missions because the enemy gets away, too many people die, you run out of time, etc. build in a civilian casualty system and a reputation meter. include some puzzle elements, force the player to make tough decisions under pressure. could be a pretty fun game imo.
Some people need to remember that violence is always an option. Not the first choice for most but still an option. Respect people before reality reminds you with an open hand