Meet the new Batman, not the same as the old Batman
The world is still recovering from its shock and horror after learning that Ben Affleck will be the next Batman. It's been a ton of fun to mock this seemingly insane casting decision with Tweets and blog posts. There are a few people sticking up for Affleck, but just about everyone else is mortified.
Affleck defenders correctly point out that previous offbeat casting decisions have worked out well for this franchise, after drawing enormous resistance from fans, including Michael Keaton as Batman and Heath Ledger as the Joker. Even the mighty Christian Bale seemed like an odd choice to people who had not seen Equilibrium.
On the other hand: Arnold Schwarzenegger as Mr. Freeze.
It's also been noted that Affleck has displayed real acting chops, including some fairly dark roles. There's no reason why the actor playing Batman has to be Batman, someone who seems like he might be one bad day away from taking on a couple of muggers in a dark alley. Playing against type - against either the bulk of your professional work, or your public image in real life - is the key to acclaim for risk-taking actors and the directors who hire them. Affleck's casting doesn't necessarily mean Batman is going back to his silly Adam West or (shudder) Joel Schumacher modes. Nothing about the tone of Man of Steel suggests that's the direction Zack Snyder wants to go.
Maybe one reason Affleck makes fans nervous is that it appears to be a frivolous, clubby casting decision for a character audiences have been taking seriously. The previous actor and director did a grand-slam job; I don't think the audience would have minded another Batman film or two from Bale and Christopher Nolan. Personally, I would have preferred Warner Bros. to have the guts to work with what Nolan left them, and continue from the end of The Dark Knight Rises. It would have been interesting to see a different person trying to be Batman in the world Nolan created, without everything Bruce Wayne brought to the table. (Especially the money. How was Joseph Gordon-Leavitt's character supposed to fix his Bat-gear when it broke?)
But Snyder said he wanted an older, experienced Batman to play against Henry Cavill's rookie Superman, building a conflict similar to the one in Frank Miller's still-unequaled Dark Knight Returns, in which an aged Batman comes out of retirement and ends up fighting Superman when the government sends the Man of Steel to put him out to pasture. If Ben Affleck turns in a good performance, in a few years people will retroactively be praising the wisdom of casting an actor in the sunset years of his leading-man era to play an older, wiser Dark Knight - who carries the scars from a thousand street battles, and finds himself wondering how he fits into a world that has a new, superhuman champion, a guy who could beat Bane by breathing on him.
If Affleck doesn't work out... well, everyone will remember he already had one chance at playing a superhero, and it didn't work out so good. Hey, wouldn't it be something if Marvel got Christian Bale in trade to play Daredevil?