Nolan apparently wanted actor Wes Bentley to play Batman:
Nolan recommends Bentley for Batman
Christopher Nolan recommends Wes Bentley for new Batman
And he had good reason. Bentley has more of that "inner turmoil, repressed rage behind the smile" intensity that Bruce Wayne is supposed to have.
The debate on Bafleck goes back and forth, but a few pictures speak a thousands words.
This looks like Wayne/Batman (image sources: IMDB):
Intense, no?
This is the "smiling on the outside, angry on the inside, I'll keep up appearances, but this is a waste of my time, and I'd rather be beating thugs into a pulp" look...
This looks like the "prematurely old soul" look of Wayne/Batman
Darnit, this is Batman!
Bentley even looks more Batman than Bale here:
But Affleck?
This man's just too happy, doesn't immediately convey that feeling of raw, keen, focused, goal-oriented intelligence... and you just can't fake inner turmoil --
not the kind Bentley has had.
Affleck has become a great director and has shown great depth as far back as "Good Will Hunting", but he's not Wayne and he's not Batman. Not in the way Bentley and a number of other actors could have been.
Nolan knows what he's talking about - and Warner Brothers should have listened.
I fear this decision might be Advantage Marvel, big-time. Here's hoping Affleck will rise to new heights.