As we keep stressing: this pairing of icons is not oil and water, it's oil and vinegar. Batman and Superman are better defined as individuals when juxtaposed to one another - and in that comparison they also form the two polar ends of the DC superhero spectrum. Batman and Superman on screen together is more than just a movie - it's a milestone.
Whether you are the geek who dreamed about, discussed and debated this event for years on end, or the casual observer who has found him/herself oddly perplexed by the question of which hero best represents your personality (Batman or Superman), this team-up is so iconic and riddled with symbolic depth that the movie will practically sell itself.
...And if Tony Stark and Nick Fury's meeting was epic enough to galvanize an Avengers universe, there's little doubt that the sheer iconography of having Superman and Batman in the same frame of film will be enough to give birth to an entire Justice League universe.