I honestly think Nolan needs to stick with the one hero vs one villain method. It gives a better exploration of both characters instead of just cluttering the screen with glorified people fighting for screen time. Batman and Robin just seemed like an orgy of stars to me, stars for star's sake rather than trying to appeal to people through good story-telling they tried to appeal through the actors, and it blew up in their faces. Nolan needs to avoid this at all costs, and despite his heavy talent in Batman Begins (Freemna, Neeson, Murphy, Oldman, Holmes) he gave the lead to someone of lesser known stature. I say keep with that trend.